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Old 12-08-2007, 04:15 AM   #16
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Ok I'm going to post the specifications from the lincoln welder site first for all to review and there will be a slight change on the kva of the transformer and breaker size from what I previously stated but the one you have chosen just fits in to the correct KVA as this welder has a higher input amperage when welding tig AC than 27 amps.... specifically 33 amps.

Here is the installation manual

http://content.lincolnelectric.com/p...r/im/im687.pdf

Ok to make a long story short the numbers may seem confusing at first 14 awg and a 50 amp breaker but you will all have to read NEC article 630 to see why this is.

(460x33)/1000 = 15.2 KVA (new transformer value)

So the transformer mentioned should squeeze in for maximum performance of the welder.

This welder has duty cycles ranging from 25% to 100% so all this figures into the wire sizing for the branch circuit conductors.

Bottom line is you use the recommended breaker or fuse size by the manufacturer.

The wire size is a minimum 14 awg and breaker is 60 amps.

But don't go going ...whoa!!.... it is permissible with arc welders when considering duty cycle for the conductors size and ocpd for the welder to strike an arc without tripping.

For the welder branch circuit I would use 60 amp breaker and 10 awg thhn in conduit instead of the 14 awg much better I think to size for the max load instead of duty cycle when dealing with an individual welder.

The key catch here is they are showing the wire size welding at 25% duty cycle but the welder is capable of 100% duty cycle so imo you can't wire the welder with 14 unless you intend to always weld a 25% duty and max output amps.

I'm a little rusty on transformer primary protection but I believe it will be 80 amps ocpd for the feeder to the transformer.... (15kva/240)(1.25)= 78 amps next size up is 80 amps requiring #4 copper thhn in conduit.
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Old 12-08-2007, 07:12 AM   #17
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Quote:
Originally Posted by Stubbie View Post
Ok I'm going to post the specifications from the lincoln welder site first for all to review and there will be a slight change on the kva of the transformer and breaker size from what I previously stated but the one you have chosen just fits in to the correct KVA as this welder has a higher input amperage when welding tig AC than 27 amps.... specifically 33 amps.

Here is the installation manual

http://content.lincolnelectric.com/p...r/im/im687.pdf

Ok to make a long story short the numbers may seem confusing at first 14 awg and a 50 amp breaker but you will all have to read NEC article 630 to see why this is.

(460x33)/1000 = 15.2 KVA (new transformer value)

So the transformer mentioned should squeeze in for maximum performance of the welder.

This welder has duty cycles ranging from 25% to 100% so all this figures into the wire sizing for the branch circuit conductors.

Bottom line is you use the recommended breaker or fuse size by the manufacturer.

The wire size is a minimum 14 awg and breaker is 60 amps.

But don't go going ...whoa!!.... it is permissible with arc welders when considering duty cycle for the conductors size and ocpd for the welder to strike an arc without tripping.

For the welder branch circuit I would use 60 amp breaker and 10 awg thhn in conduit instead of the 14 awg much better I think to size for the max load instead of duty cycle when dealing with an individual welder.

I'm a little rusty on transformer primary protection but I believe it will be 80 amps ocpd for the feeder to the transformer.... (15kva/240)(1.25)= 78 amps next size up is 80 amps requiring #4 copper thhn in conduit.
Hi Stubbie.

I based my initial calculation on 30 Amps @ 480 volts, since 480 volts will be the applied voltage. Since the max current drawn will be 33 Amps & the applied voltage will be 480 volts (a 2:1 ratio transformer), the kVA will be 15.84. Or is the supply voltage a guaranteed 230 volts?

Do you use "motor start" circuit breakers/fuses in the States? In Australia, the secondary of the transformer would be protected by either "motor start" type circuit breakers or HRC fuses, with a standard overload capacity of the FLA (33 Amps). Since a 33 Amp CB or fuse is not available, the next size up would suffice & of course, the minimum cable size would be governed by the OCPD. In Australia, only the transformer secondary need be protected by an OCPD that relates directly to the current output of the transformer. The cable to the primary is protected by the supply circuit breaker.

I see that you mention a figure of 1.25 in your calculations. This figure relates only to thermal overload protection (generally attached to contactors) used for motors/transformers etc. It does not relate to circuit breakers/fuses because each different brand of circuit breaker/fuse can have different time/current curves whereas thermal overloads are governed by one standard. So, if a thermal overload is used to protect a motor etc, it should be set at 125% (1.25) the FLA.


EDIT: Just noticed the tables in your above post. Just as a comparison, here are the Australian current ratings used for 2c+e double insulated (PVC) cables "enclosed in air" (not in any type of insulation);

1.5 mm2 cable - 15 amp maximum circuit breaker.
2.5 mm2 cable - 20 amp maximum circuit breaker.
4 mm2 cable - 25 amp maximum circuit breaker.
6 mm2 cable - 32 amp maximum circuit breaker.
10 mm2 cable - 40 amp maximum circuit breaker.
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Old 12-08-2007, 09:19 AM   #18
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Single phase at 460 and 575. Now thats something. I guess you learn something hopefully everyday.

General Purpose? Less money too. Delta/Delta
He could even go for the aluminum core....even less money.
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Old 12-08-2007, 11:43 AM   #19
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Good Morning from Kansas elkangarito...

Well its a long story trying get through the differences and things that aren't so different between our systems. Arc type Welders are different duck in the way we work with them. The NEC primarily addresses welders in an industrial or commercial situation. This is commercial but a single welder so we don't have a feeder to serveral welders. This is also a non motor generater welder. So the nec allows for down sizing of the branch circuit conductors based on a series of multipliers and duty cycles of a welder. For example if we take the lowest duty cycle of this welder 25% and the max rated input amps of 33 the factor is .55 so .55(33) = 18 amps. Our #14 copper is rated 20 amps and we can stick a 200% ocpd on that based on the input amperage off 33 which gives us 66 amps. So the manufacturer is stating 14 awg copper in conduit (makes a difference vs some cables). This is to allow the welder to "start" so to speak without tripping the ocpd. The welder has integral overload protection. So thats the short of it.



The transformer is 15 KVA and no you will probably get more than 230 volts but that depends on what you have at the facility generally we have 235 volts in my area. Thats why I was saying it squeezes the limit. I would think the transformer company your purchasing from could get that figured out for you as to the kva you will need.

For discussion

The transformer is a different story your going to be feeding it 240 volts and that is the P-line voltage or primary side in this case. The tranny as you call it is protected at 125% of its kva based on the input and output voltages and continuous load. Thing is on the secondary side (460) volts your going to be feeding the welder and only the welder.. no panelboards. So if your tap conductors are 10 feet or less before they hit the termination point, in this case the 60 amp breaker at the disconnect so they are not required to have overcurrent protection based on the transformer rating....I think. It's been a while since I have dealt with this situation. You are however required to have the tap conductors sized greater than the device they terminate on. So the secondary conductors would need to be #6 copper in conduit between the secondary and the disconnect of 60 amps. Then from there to the welder they could be 14 awg copper according to the manufacturer. Anyway it would be best for chcustom to get professional help on his end to wire this transformer up to code as I would not want to say this is how it would be done. This is for sake of discussion between you and me and who ever else wants to join in....

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Old 12-08-2007, 02:21 PM   #20
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Quote:
Originally Posted by Stubbie View Post
Good Morning from Kansas elkangarito...

Well its a long story trying get through the differences and things that aren't so different between our systems. Arc type Welders are different duck in the way we work with them. The NEC primarily addresses welders in an industrial or commercial situation. This is commercial but a single welder so we don't have a feeder to serveral welders. This is also a non motor generater welder. So the nec allows for down sizing of the branch circuit conductors based on a series of multipliers and duty cycles of a welder. For example if we take the lowest duty cycle of this welder 25% and the max rated input amps of 33 the factor is .55 so .55(33) = 18 amps. Our #14 copper is rated 20 amps and we can stick a 200% ocpd on that based on the input amperage off 33 which gives us 66 amps. So the manufacturer is stating 14 awg copper in conduit (makes a difference vs some cables). This is to allow the welder to "start" so to speak without tripping the ocpd. The welder has integral overload protection. So thats the short of it.



The transformer is 15 KVA and no you will probably get more than 230 volts but that depends on what you have at the facility generally we have 235 volts in my area. Thats why I was saying it squeezes the limit. I would think the transformer company your purchasing from could get that figured out for you as to the kva you will need.

For discussion

The transformer is a different story your going to be feeding it 240 volts and that is the P-line voltage or primary side in this case. The tranny as you call it is protected at 125% of its kva based on the input and output voltages and continuous load. Thing is on the secondary side (460) volts your going to be feeding the welder and only the welder.. no panelboards. So if your tap conductors are 10 feet or less before they hit the termination point, in this case the 60 amp breaker at the disconnect so they are not required to have overcurrent protection based on the transformer rating....I think. It's been a while since I have dealt with this situation. You are however required to have the tap conductors sized greater than the device they terminate on. So the secondary conductors would need to be #6 copper in conduit between the secondary and the disconnect of 60 amps. Then from there to the welder they could be 14 awg copper according to the manufacturer. Anyway it would be best for chcustom to get professional help on his end to wire this transformer up to code as I would not want to say this is how it would be done. This is for sake of discussion between you and me and who ever else wants to join in....
Good morning to you Stubbie. I didn't know you were from Kansas! The only thing I can say from an uneducated aussy's point of view is something that Judy Garland said..."Toto, are we really home?" Then again, maybe my quote is wrong.

Anyway, I got your drift about what you are saying but one thing still causes me a problem...the size of the secondary protection.

Disregarding duty cycles & cable sizes, the transformer is capable of a certain output. In this case, we assume a maximum output of 33 Amps (not an ideal figure). The real problem now is to adequately protect the secondary windings. The only way this can be done is by ensuring that the maximum amount of current that can flow through those windings does not exceed the output rating of the transformer...in this case, 33 Amps. Since the wire used in the secondary winding of the transformer will be such that it can handle more than 33 Amps (maybe 40 Amps), the ideal situation would be to provide an OCPD that will trip below this figure (less than 40 Amps for example). Disregarding what the NEC says, calculation & the use of appropriately sized OCPD's will properly protect the transformer & the equipment, since most OCPD's in this situation will be rated less than that of the NEC requirement.

Stubbie, I'm not disagreeing with you. What I am saying is that if "motor start" circuit breakers (usually Curve 1) or fuses are used, they will perform much better than an oversized circuit breaker/fuse.

I don't want to seem as if I'm blowing this out of my bum but in Australia, using a 60 Amp fuse to protect a 33 Amp circuit is crazy...unless the rating of this particular USA 60 Amp fuse is different? Perhaps the US regs rate a 60 Amp fuse (time lag type - same as motor start) as a peak rating? I don't know. All I know is that "motor start" OCPD's in Australia are rated for FLA, so as not to confuse the issue.

I think this may be a bit confusing so I'll try to summerise;

1] The secondary of the transformer needs to be protected. This can only be done by using an OCPD that is rated according to the FLA of the transformer. Using an OCPD with a higher value may risk damage to the transformer.

2] Whilst OCPD's are ultimately designed to protect the cable in this instance (according to the regs), there is no reason that an OCPD cannot exceed the requirement of the regs (which is what I would be doing unless I want to risk a very expensive transformer).

Don't you have "motor start" fuses/circuit breakers whereby the rating(s) is/are given in FLA? My god you live in a confusing world! I'm glad I'm not an American sparky.
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Old 12-08-2007, 04:43 PM   #21
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Yes I see your point the tranny is making it interesting. And don't worry about disagreeing with me.... it is just possible I could be wrong...is that clear....mate

Btw....that bold "real" problem struck my funny bone....

I understand your confusion on the ocpd being so large it is sorta like motors ocpd holding for the inrush at start up we can have 40 amp ocpd on 12 awg wire in the usa.... there are exceptions of course. Yes our breakers are motor start to a degree....they are inverse time in relation to current inrushes in that they will delay opening....in industrial applications this can change and fuses may be required. I'm not sure how to post a short answer...... Let me post this diagram below and may be you see my problem with the secondary protection in this case. If we were supplying a panelboard full of breakers the NEC would require secondary protection.

If you can get to this link it will explain better than I.......

http://ecmweb.com/mag/electric_trans...allation_made/

Also go back to post #16 I completely forgot to add the reason for using the 10 awg in conduit. I have it in bold print. It is kind of a goofy way to list the wiring of the welder by the manufacturer. It could really cause the 14 to get hot if you welded at 100% duty on 14 awg.... I believe this is what you were also saying by your earlier calculations.

BTW.. that was the correct quote from the Wizard Of Oz and Dorothy. How is that bloke Mick Dundee doing? I seem to remember he passed away? Shame if thats the case.
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Old 12-09-2007, 11:42 AM   #22
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Originally Posted by Stubbie View Post
Yes I see your point the tranny is making it interesting. And don't worry about disagreeing with me.... it is just possible I could be wrong...is that clear....mate

Btw....that bold "real" problem struck my funny bone.

I understand your confusion on the ocpd being so large it is sorta like motors ocpd holding for the inrush at start up we can have 40 amp ocpd on 12 awg wire in the usa.... there are exceptions of course. Yes our breakers are motor start to a degree....they are inverse time in relation to current inrushes in that they will delay opening....in industrial applications this can change and fuses may be required. I'm not sure how to post a short answer...... Let me post this diagram below and may be you see my problem with the secondary protection in this case. If we were supplying a panelboard full of breakers the NEC would require secondary protection.

If you can get to this link it will explain better than I.......

http://ecmweb.com/mag/electric_trans...allation_made/

Also go back to post #16 I completely forgot to add the reason for using the 10 awg in conduit. I have it in bold print. It is kind of a goofy way to list the wiring of the welder by the manufacturer. It could really cause the 14 to get hot if you welded at 100% duty on 14 awg.... I believe this is what you were also saying by your earlier calculations.

BTW.. that was the correct quote from the Wizard Of Oz and Dorothy. How is that bloke Mick Dundee doing? I seem to remember he passed away? Shame if thats the case.
Hi Stubbie.
Thank god I got something right...the bit about the Wiz of Oz .

Anyway, I was able to download your link (for a change) & I can understand your dilemma. For me, however, there is no dilemma. I'm sure you'll agree that the "code" (like all codes) dictate a minimum standard. Therefore, "technically" exceeding this minimum standard should not be a problem.

Just to make sure I've got things clear & that we understand each other, here is how I see the situation;

1] suggested minimum size of transformer (2:1 step up) based on a 240 volt Primary @ 33 Amps FLA Secondary current - 16kVA.

2] equipment that needs to be protected - cable to the Tx primary, cable from the Tx secondary, the welding unit.

3] supply - single phase 240 volts.

My assumptions will also be based on a transformer inrush current that will be between 2.5 to 4 times the FLA. Also, "duty cycle" will be assumed to be 100% since this cannot be governed in any practical way.

The cable to the Primary winding needs to be protected. 20 Amp cable could be the minimum size supply cable but 32 Amp cable is preferred. It can be protected by one of 2 means;
1] a "motor start" rated circuit breaker'
2] a "motor start" rated HRC fuse.

If either of these devices are used, the cable size need only be that of the OCPD. For example, a 32M40 Type 'T' GEC fuse could be used to protect the Primary supply cables. This means that the the fuse has a continuous rating of 32 Amps (for cable protection etc) & a time/current protection rating for "motor start". The minimum sized cable that can be used with this fuse is 32 Amp.
Thermal magnetic circuit breakers are slightly different in that their size will be larger to handle the inrush current, which leads to larger cable sizes. This is not so if a Hydraulic Magnetic circuit breaker is used. These type of circuit breakers a much more accurate & stable compared to the thermal magnetic type. Also, they will afford the same cable size "savings" as a "motor start" HRC fuse. I used to work for Heinemann Electric, who manufactures these breakers. They are the Rolls Royce while the thermal magnetic type are the Hyundai.

I recommend that both cables from the Tx Secondary be protected with "motor start" HRC fuses as such - GEC Type 'T' 63M80. This means that the Secondary cable must be sized to handle 63 Amps minimum. I also recommend that the Primary 'hot' cable be protected by a GEC Type 'T' 32M40 fuse & this cable must be sized to handle 32 Amps minimum.
These fuses will provide adequate Short Circuit & Overload protection. As far as protecting the welder (if required), I would use a DOL starter with thermal overload protection.

This may seem extreme but the cost of the transformer & the welder may well & truly warrant this type of protection. If it were my welder, I'd do it this way.

What do ya reckon mate?

GEC fuse info here - http://www.ip.alstom.com.au/Download...se%20Links.pdf

EDIT: I've just realised that I made a BIG mistake with the Primary current/supply conductor calculation - it should be about 70 Amps. Therefore, the GEC Type 'T' fuse should be a 100M125, which means that the supply cable to the transformer should be a minimum capacity of 100 Amps. I'm so used to transformers being "step down".
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Old 12-09-2007, 12:34 PM   #23
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Now to try and explain the big breaker on small wire for an arc welder. It boils down to a fixed duty cycle. If we have an arc welder that has an input of 40 amps at a rated output of 150 amps and a duty cyle of 20% we are allowed to downsize the conductors. The downsizing factor for 20% duty cycle is .45. So with this example welder .45(40) = 18 amps. So I am allowed to use 20 amp rated 14 awg thhn copper wire in conduit to serve this welder. This is because 20% duty means that I can weld continuously for 2 minutes out of a 10 minute period at maximum rated input amperage before the welder requires cooling. Cooling time is 8 minutes (10 minutes - 2 minutes). Then I can weld again. Some welders have duty cycle protection so they will not work if the duty cycle is exceeded. This machine does have duty cycle protection that we are talking about in this thread with chkustom. They also have internal overload protection in most cases. If they don't then overload protection must be provided at a disconnect in the form of fuses to protect the welder. So a welder with 20% duty cycle and the proper overheating protection in place will not overheat 14 awg wire in normal operation even though the 40 amp breaker may allow over amperage to occur for brief periods. And you have to remember the rating of the welder is at maximum amps and most output amps so you will not always be at those levels in a lot of your welding. Your welding requirements will vary over a wide range of input amperages.
Ok now the big breaker issue. In my example the minimum breaker is 40 amps but the manufacturer may say 50 amp recommended on 14 awg. Sounds crazy but is allowed. And the nec says you can increase the breaker to 200% over the max. nameplate input amps. all of this is about the characteristics of the particular welder. In that the manufacturer knows that nuisance tripping will not occur at their recommended breaker size when you start your arc or during welding. Heck the NEC would allow an 80 amp breaker in this situation. Probably would never need to do that but it is allowed.
Now why they don't just tell you to use #8 awg copper for the maximum input amperage and a 40 or 50 amp breaker I can't tell you but I always recommend this in any residential or light commercial use of an individual welder.... because I am a firm believer in operator error and murphys law.

The deal with this thread is the rating by the manufacturer at a 25% duty cycle at maximum output amps but the welder has varying duty cycles.....up to 100% duty at lower output amps during the welding process. Not knowing what the input amps are at 100% duty makes using 14 awg not feasible IMO. Now I haven't looked at all the available data and spec's on this welder so there may be a amperage vs duty cylce chart that would allow us to determine the input amperage at 100% duty cycle. If thats around 20 amps then I would be ok with 14 or 12 awg in conduit on a 60 amp breaker in this welders case. Without that information then I would use 10 awg in conduit on a 60 amp breaker which is the recommended breaker by the manufacturer. Our 10 awg copper thhn wire has a 35 amp rating at 75C when terminated on equipment with like temperature ratings.

FYI .. most other cases except welders and motors we protect 14 awg on 15 amp breakers, 12 awg on 20 amp breakers and 10 awg on 30 amp breakers.

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Old 12-09-2007, 01:02 PM   #24
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Hi elkangarito....

I must have been deep in thought when you posted. Snowing here in Kansas today....no tornadoes...

You know I have no problem at all with what you posted so I am not going to argue one bit... it makes perfect sense to me. I think it just boils down to differences in the way our countries do things with certain applications.

OUr original poster hasn't come back yet ... maybe we scared him.....

I also agree the xfmer should be minimum 16kVA....
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Old 12-09-2007, 01:19 PM   #25
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Hi Stubbie, my comments in blue.

Quote:
Originally Posted by Stubbie View Post
Now to try and explain the big breaker on small wire for an arc welder. It boils down to a fixed duty cycle. If we have an arc welder that has an input of 40 amps at a rated output of 150 amps and a duty cyle of 20% we are allowed to downsize the conductors. The downsizing factor for 20% duty cycle is .45. So with this welder .45(40) = 18 amps. So I am allowed to use 20 amp rated 14 awg thhn copper wire in conduit to serve this welder. This is because 20% duty means that I can weld continuously for 2 minutes out of a 10 minute period at maximum rated input amperage before the welder requires cooling. Cooling time is 8 minutes (10 minutes - 2 minutes). Then I can weld again. Some welders have duty cycle protection so they will not work if the duty cycle is exceeded. They also have internal overload protection in most cases. If they don't then overload protection must be provided at a disconnect in the form of fuses to prevent overheating the welder. So a welder with 20% duty cycle and the proper overheating protection in place will not overheat 14 awg wire in normal operation even though the 40 amp breaker may allow over amperage to occur for brief periods. And you have to remember the rating of the welder is at maximum amps and most output amps so you will not always be at those levels in a lot of your welding. Your welding requirements will vary over a wide range of input amperages.

Understood but for me, there are too many "unknowns" in this situation. I would choose to "cover my bum" 100%. This means assuming a possible 100% duty cycle. For me, the issues in descending order of importance are;

1] Primary (supply) & Secondary cable protection.
2] Transformer protection.
3] Welding unit protection.

Ok now the big breaker issue. In my example the minimum breaker is 40 amps but the manufacturer may say 50 amp recommended on 14 awg. Sounds crazy but is allowed. And the nec says you can increase the breaker to 200% over the max. nameplate input amps. all of this is about the characteristics of the particular welder. In that the manufacturer knows that nuisance tripping will not occur at their recommended breaker size when you start your arc or during welding. Heck the NEC would allow an 80 amp breaker in this situation. Probably would never need to do that but it is allowed.
Now why they don't just tell you to use #8 awg copper for the maximum input amperage and a 40 or 50 amp breaker I can't tell you but I always recommend this in any residential or light commercial use of an individual welder.... because I am a firm believer in operator error and murphys law.

Yes, fully agree with Murphys' Law & thus my "over cautious" reaction. As far as breaker/cable sizes are concerned, I'd be ignoring the NEC & going for a reduced breaker size. This can only be achieved by using proper motor start breakers or even better, motor start HRC fuses. By using the correct OCPD, you can save on cable (size) & exceed the NEC specification without introducing "nuisance tripping" into the equation. I'm always concerned when an OCPD is rated so that it may not actually protect the cable that it supplies. This is generally only allowed (in Australia) if the equipment being supplied is considered an "essential service" ie fire equipment, lifts etc. For a welding unit, I'd make sure that the cable is adequately protected, disregarding what the code says.

The deal with this thread is the rating by the manufacturer at a 25% duty cycle at maximum output amps but the welder has varying duty cycles.....up to 100% duty at lower output amps during the welding process. Not knowing what the input amps are at 100% duty makes using 14 awg not feasible IMO. Now I haven't looked at all the available data and spec's on this welder so there may be a amperage vs duty cylce chart that would allow us to determine the input amperage at 100% duty cycle. If thats around 20 amps then I would be ok with 14 or 12 awg in conduit on a 60 amp breaker in this welders case. Without that information then I would use 10 awg in conduit on a 60 amp breaker which is the recommended breaker by the manufacturer. Our 10 awg copper thhn wire has a 35 amp rating at 75C when terminated on equipment with like temperature ratings.

Sorry Stubbie but I've gotta disagree about the duty cycle thing. If there is no electrical or mechanical control of the duty cycle, I'd be assuming a 100% rating to cover my bum. Besides, this is only a short cable length (I assume) & so the cost of heavier cable is insignificant. Perhaps the OP can give us more info as to whether the duty cycle is controlled or not?

FYI .. most other cases except welders and motors we protect 14 awg on 15 amp breakers, 12 awg on 20 amp breakers and 10 awg on 30 amp breakers.
In Australia, no such complex problems occur with such devices. The Australian Wiring Rules directly relate to the reality of the load equipment & the supply conductors ie if there is no electrical or mechanical way to control the duty cycle of a given device, it shall be rated at 100% duty cycle. Also, the use of OCPD's that fit the application are also encouraged. In this case, "motor start" OCPD's could be used as long as overload & short circuit currents are catered for.
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Old 12-09-2007, 01:28 PM   #26
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Hi elkangarito....

I must have been deep in thought when you posted. Snowing here in Kansas today....no tornadoes...

You know I have no problem at all with what you posted so I am not going to argue one bit... it makes perfect sense to me. I think it just boils down to differences in the way our countries do things with certain applications.

OUr original poster hasn't come back yet ... maybe we scared him.....

I also agree the xfmer should be minimum 16kVA....
Sorry mate...just posted a comment & now I've seen your (this) post.
You can have that bloody snow...I hate the stuff. Here in wonderful Thailand, the temp NEVER drops below 25 degrees C. Now, it's about 28 deg C & it's 20 minutes past 2 in the morning (Monday..today is a public holiday).

You're right about "country" differences but thankfully, the same laws of physics etc apply equally in all countries. I was simply applying electrical calculation to the situation. I'm sure you'll agree that on many occasions, a "code" is not always the answer. Sometimes, one has to do a bit of calculation to find out the best solution. As long as the solution falls within the boundaries of the code, all is well.

EDIT: I've just realised that I made a BIG mistake with the Primary current/supply conductor calculation - it should be about 70 Amps. Therefore, the GEC Type 'T' fuse should be a 100M125, which means that the supply cable to the transformer should be a minimum capacity of 100 Amps. I'm so used to transformers being "step down". Sorry.
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Last edited by elkangorito; 12-09-2007 at 01:39 PM.
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Old 12-09-2007, 04:01 PM   #27
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Had to go to the grocery store, we Americans do eat ya know! Yes I absolutely agree on the duty cycle as you explained it. I disagree with how the manufacturer listed the wire size and breaker size that to me was an oversight on whoever wrote those instructions. In the end it looks like we aren't to far apart on our thinking as I to would size this welder at at 100% duty cycle. This lincoln welder does have duty cycle control and will shut down the welding circuit if overheated until the thermal limit reopens the circuit. it's in the wiring diagram and buried in the instructions. It's very interesting to me on the differences we have on ocpd for motors and welders. It is very common for us in industrial settings to be very much like you guys in that we commonly use motor starters and fuse protection for overload. But this is due mainly to 3 phase applications vs. single phase applications. In our HVAC it is very common for the manufacturer to list a maximum breaker size on the equipment nameplate that is much bigger than the ampacity of the supply conductors. But that doesn't mean you have to go with the max breaker as listed you can go smaller. This welder for instance is not required to go with a 60 amp breaker, you can go with a smaller breaker. So one could install a 35 or 40 amp breaker and see if it would hold.... but I'll tell ya in most cases the manufacturer is giving you the necessary breaker size to to avoid any nuisance tripping.

I also agree if you have no duty cycle protection and that is left up to the operator then you bet necessary protection better be installed in the circuit or your going to have 'murphy' pay you a visit.

And yes this step up single phase thing with this transformer is not something I have dealt with much either.


Great discussion.... enjoyed it


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Old 12-10-2007, 09:36 PM   #28
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Must agree...always interesting to get into the "nuts'n'bolts" of it.

Also, after I read your last post, I did notice the bit in the welder spec about the duty cycle control. I'm never comfortable with these assumptions...a maximum of about 70 Amps will be flowing through the Primary side cable no matter what the equipment duty cycle is.

So, what would you recommend? Depending upon the type of OCPD used, the Primary side cable could be as small as 70 Amps or as large as 100 Amps. The Secondary side cable could be as small as 35 Amps or as large as 63 Amps. If "curve 1" breakers are used (Hydraulic), the smaller cable sizes can generally be used. The use of HRC fuses requires the bigger cable sizes.

If it was me, I'd be sourcing some Heinemann "curve 1" breakers so as to save on cable size. You should be able to get these breakers in the states as Heinemann was originally an American company.
If maximum protection/safety is required, I'd stick with the fuses.

What do ya reckon, mate?
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Old 12-10-2007, 10:40 PM   #29
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I'd protect the secondary at 40 amps with an inverse time thermal magnetic breaker or yes you could use a curve 1 hydraulic/magnetic. I'd protect the primary at 80 amps.

I'd put the welder on 35 amp wire and a 40 amp inverse time breaker. Remember this welder has internal integral overload/thermal protection whether for duty cycle or for equipment fault.

FYI in the USA you will rarely see a hydraulic breaker at the commercial level they are almost always used at the industrial level ...however they are becoming more popular for the reasons you listed.

Heinemann is now eaton electric of Canada.

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