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Old 05-09-2011, 08:58 PM   #1
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Sub-panel for 3 space heaters


Hello Electric Experts,

I have questions, questions and more questions.

I am planning to extend my 200A main panel to a sub-panel about 40 feet away. The sub-panel will power three (for now) space heaters . All heaters are 240 VAC appliances and require 15A, 15A and 25A. I expect to connect these heaters to two 20A 2-pole breakers and one 30A 2-pole breaker, using something like a Square D HOM612L100 breaker panel or, if I need a main breaker, perhaps a Square D HOM816M100 panel.

In the main panel I expect to use a 70A, 80A, 90A or 100A 2-pole breaker to feed the sub-panel.

[Q0] I use Square D Homeline equipment because it is conveniently available at a Home Depot and it is cost effective. Should I consider other brands?
[Q1] What size wire do I need for 70A, 80A, 90A or 100A service?
[Q2] Since all appliances are 240 VAC, do I need to run a neutral in addition to a ground?
[Q3] If I enclose the service wiring in EMT, do I need a separate ground wire?
[Q4] Should I connect an earth ground rod directly to the sub-panel? What diameter rod? What size conductor?
[Q5] What determines whether I need a main breaker in the sub-panel?
[Q6] I can increase the number of circuits in a breaker panel by using "twin" 2-pole breakers. Is there a disadvantage to using twins?

The heaters are within 15 feet of the sub-panel. The docs for the heaters state that I should use #12 / #8 wiring for the 15A / 25A heaters. Some of the wiring to the heaters will be under the floor, so I would use UF cable in this case.
[Q7] Are there tools for cutting away the outer sheath on electrical cables and stripping the leads? Recommendations would be most appreciated.
[Q8] Does it meet code to mount terminal strips in junction boxes for connecting heater wiring to source wiring (heating element, fan and control pairs)? I would prefer terminal strips to wire nuts or crimping leads.
[Q9] Between sub-panel and heaters, can high current wires (heating element) be run in the same conduit as low current wires (fan, control)?
[Q10] Between main panel and sub-panel, can low current wires be run in the same conduit with sub feed cables?
[Q11] How long should I leave the leads in heater junction boxes to pass inspection?

Any other comments on my approach would be welcome.

Now if only I could remember the latest edition of the NEC!

Thank you very kindly for sharing your knowledge and experience.
Daneel

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Old 05-09-2011, 09:08 PM   #2
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Sub-panel for 3 space heaters


Definitely get your hand on a current NEC. Also, verify what codes your local jurisdiction uses.

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Old 05-09-2011, 09:59 PM   #3
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Sub-panel for 3 space heaters


Quote:
Originally Posted by Daneel View Post
Hello Electric Experts,
[Q0] I use Square D Homeline equipment because it is conveniently available at a Home Depot and it is cost effective. Should I consider other brands?

That's fine.

[Q1] What size wire do I need for 70A, 80A, 90A or 100A service?

Depends on the type of wire. It will be something between #4 copper and 1/0 aluminum.

[Q2] Since all appliances are 240 VAC, do I need to run a neutral in addition to a ground?

Yes, just in case.

[Q3] If I enclose the service wiring in EMT, do I need a separate ground wire?

No, the EMT can serve as the grounding means.

[Q4] Should I connect an earth ground rod directly to the sub-panel? What diameter rod? What size conductor?

No. Assuming the subpanel is in the same building as the main, you do not need (nor should you have) a separate ground rod. Also note that you must not bond neutral and ground in the subpanel.

[Q5] What determines whether I need a main breaker in the sub-panel?

You don't. It's strictly a matter of personal preference, if you want to have a way to shut down the whole subpanel without walking back to the main panel. The breaker feeding the sub from the main panel provides overcurrent protection.

[Q6] I can increase the number of circuits in a breaker panel by using "twin" 2-pole breakers. Is there a disadvantage to using twins?

You cannot use tandem breakers for 240V circuits. Both halves of the twin connect to the same hot bus, so they have zero volts between them instead of the 240V you're looking for. You can use quad breakers, however, if they are available for your panel. Quads are pairs of tandems that form two double-pole circuits per breaker.

As a side note, I noticed that you planned on using 30A breakers for circuits with 25A heater loads. That's not code compliant. For circuits with continuous loads (heaters are defined as continuous, regardless of whether they actually are or not), the load cannot exceed 80% of the breaker or wire ampacity. So, a 20A breaker and #12 wire is fine for a 15A load, but you need to jump up to 40A and #8 wire for the 25A circuits.

The heaters are within 15 feet of the sub-panel. The docs for the heaters state that I should use #12 / #8 wiring for the 15A / 25A heaters. Some of the wiring to the heaters will be under the floor, so I would use UF cable in this case.

You can use UF, or you can use THWN in conduit. Either way.

[Q7] Are there tools for cutting away the outer sheath on electrical cables and stripping the leads? Recommendations would be most appreciated.

There are all sorts of cable sheath stripping tools out there. Most are only marginally useful. For stripping NM, the cheap pressed steel thingies work as well as anything else. For UF cable, nothing works well. It's just tough. For stripping the conductors themselves, I use wire cutters almost all the time (or a box cutter for large conductors) - but I have a lot of practice. Most reasonably well made strippers out there are good for 10-14AWG wire. Larger than that is usually best done with a sharp blade.

[Q8] Does it meet code to mount terminal strips in junction boxes for connecting heater wiring to source wiring (heating element, fan and control pairs)? I would prefer terminal strips to wire nuts or crimping leads.

If the terminal strips are UL listed for that purpose, then it would be code compliant. However, they are probably not. Wire nuts would be much more normal. Also note that most terminal strips require the use of ring or spade terminals instead of bare conductors, so you'd have to crimp stuff anyway.

Why are those connections not already done inside the heaters? Most heaters have only a single-point connection for power. Keep in mind that all conductors on those circuits must be sized to match the breaker rating. You cannot use less than #8 wire on a 40A breaker, for example, even if it's running to the fan and only has a 1A load. That's one reason those connections are usually done internally in the appliance.


[Q9] Between sub-panel and heaters, can high current wires (heating element) be run in the same conduit as low current wires (fan, control)?

Yes, assuming they are all line-voltage. Low-voltage cabling must be in separate conduit usually.

[Q10] Between main panel and sub-panel, can low current wires be run in the same conduit with sub feed cables?

Yes, but it's not generally done. It's easier to run multiple conduits. Otherwise you have to pull all the conductors in at once and it's very hard to replace any of them or add more later.

[Q11] How long should I leave the leads in heater junction boxes to pass inspection?

They must extend at least 6" out of the box.
... at least five characters out of the quote.
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Old 05-09-2011, 10:18 PM   #4
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Sub-panel for 3 space heaters


Wowie this will fill pretty good part so all my answer will be in bleu.

Quote:
Originally Posted by Daneel View Post
Hello Electric Experts,

I have questions, questions and more questions.

I am planning to extend my 200A main panel to a sub-panel about 40 feet away. The sub-panel will power three (for now) space heaters . All heaters are 240 VAC appliances and require 15A, 15A and 25A. I expect to connect these heaters to two 20A 2-pole breakers and one 30A 2-pole breaker, using something like a Square D HOM612L100 breaker panel or, if I need a main breaker, perhaps a Square D HOM816M100 panel.

In the main panel I expect to use a 70A, 80A, 90A or 100A 2-pole breaker to feed the sub-panel.

[Q0] I use Square D Homeline equipment because it is conveniently available at a Home Depot and it is cost effective. Should I consider other brands?
A. I rather try to match to the exsting load centre unless you have FPE or Zinsco then use other brandname.

[Q1] What size wire do I need for 70A, 80A, 90A or 100A service?
A. It depending on the exsting load you have in the exsting load centre do you have spa or any super high power useage appalices or others??

[Q2] Since all appliances are 240 VAC, do I need to run a neutral in addition to a ground?Oui please do due you mention may add other circuits in future.

[Q3] If I enclose the service wiring in EMT, do I need a separate ground wire?
It depending on the layout of EMT but if done properly no it do not need grounding conductor but for myself I rather run it anyway for safety issue in case the connector or coupling become loose.

[Q4] Should I connect an earth ground rod directly to the sub-panel? What diameter rod? What size conductor?
Nope you don't need it due you are in the same building however you have to keep the ground and netural seperated in the subpanel and you may end up buy a grounding bussbar due some may not included in there.
[Q5] What determines whether I need a main breaker in the sub-panel?
It depending on the numbers of "throws" in the subpanel (this part may change per local codes so check it out )
[Q6] I can increase the number of circuits in a breaker panel by using "twin" 2-pole breakers. Is there a disadvantage to using twins?

I don't think so due that subpanel you posted that can take the twinners however this can get very tricky with it so I will suggest to use diffrent model like 20 space sans main breaker that will work however some big box store will stock 100 amp 20 space with main breaker cheaper than sans main breaker

The heaters are within 15 feet of the sub-panel. The docs for the heaters state that I should use #12 / #8 wiring for the 15A / 25A heaters. Some of the wiring to the heaters will be under the floor, so I would use UF cable in this case.

For the electrique heaters if you going with #12 AWG size keep it to 16 amp (3840 watts @ 240 volts ) and per NEC code the electrique baseboard heater are contiounus useage so they are derated.

As far for under the wooden floor the NM cable will work just fine unless you are under the slab (cement floor ) then use the PVC conduit with THHN/THWN conductors.

[Q7] Are there tools for cutting away the outer sheath on electrical cables and stripping the leads? Recommendations would be most appreciated.

There are few diffrent tools you can get them in big box store the wirestipper is pretty common item I think they run about 15 Euros or so.
[Q8] Does it meet code to mount terminal strips in junction boxes for connecting heater wiring to source wiring (heating element, fan and control pairs)? I would prefer terminal strips to wire nuts or crimping leads.
It can if you have room for it and for termail strips you will need much larger box anyway.

[Q9] Between sub-panel and heaters, can high current wires (heating element) be run in the same conduit as low current wires (fan, control)?
Most case yes if the fan and control wire is line voltage or run the thermosat wire in seperarted conduit this is genrally safer this way.
[Q10] Between main panel and sub-panel, can low current wires be run in the same conduit with sub feed cables?
It can be done however the derateing will come in the play with the numbers of conductors in the conduits.
[Q11] How long should I leave the leads in heater junction boxes to pass inspection?
It depending on the heater itself and the leads is the same as standard switch but leave it little longer than useal
Any other comments on my approach would be welcome.

Now if only I could remember the latest edition of the NEC!

What state ya you are in ? there is couple diffrent NEC verison going out on all states

Thank you very kindly for sharing your knowledge and experience.
Daneel
If you have more question just holler one of us will give you more answer and also please do the load demand caluation on the heater and the main panel so we can able assist you on the conductor sizing between the main and sub panels.

Merci,
Marc
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Old 05-09-2011, 10:27 PM   #5
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Sub-panel for 3 space heaters


You will need to run a neutral, and you shouldn't run any cable within conduit. The rating for cable is for open air situations. And you need to bond the ground to the sub panel, but not the neutral. The ground must be bonded only at the main panel. I think it's very smart to have a seperate panel for the heat. I would put the panel on a 100 qmp breaker, using #4 for the feeders, and #8 for the ground. THHN, not THWN (#4 is allowed for a 100amp feeder, but not a 100amp circuit)
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Old 05-11-2011, 06:43 AM   #6
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Sub-panel for 3 space heaters


Vive La France, Maryland and Missouri!

Thank you Leah, mpoulton, Marc and Missouri Bound for taking time to respond. This chatroom is a wonderful resource. I am learning a lot from scanning posts.

[Q0.1] I have downloaded my state electrical code. No FPE or Zinsco stuff. The 200A Challenger panel is exclusively for off-peak heating. The panel was populated with unused breakers (Challenger, Siemens and Type MP-T/E82615, possibly Murray) by a licensed electrician. I assume/hope that breakers have been officially tested with the panel. I will probably go with a Square D subpanel because it matches the house main panel, so if radical electrical changes happen it can be re-used elsewhere. And will look for a Challenger or Siemens 2-pole breaker for the feeders.

[Q1.1] I consider my space heater installation project to be "temporary" in the sense that heater locations may be changed. This depends on family consensus -- unpredictable as to when improvements will be improved and by how much. I want to do this work to code but as inexpensively as possible. Hence my ambivalence about feeder Amps.

[Q2.1] No 120 VAC devices in the future, possibly more space heater(s) but only up to the maximum total continuous current allowed for the subpanel. So no neutral needed, right?

[Q3.1] I will use EMT or PVC with diameter calculated per the conduit fill calculator at:
www.onlineconveyorparts.com/enghelp/conduit.htm

[Q6.1] I see that according to NEC 210.19(A)(1), "... the minimum branch-circuit conductor size ... shall have an allowable ampacity not less than the noncontinuous load (zero) plus 125% of the continuous load (125% of 25A = 31.25A)." I will use 40A breakers for 25A heaters.

For all three space heaters, continuous loads total 15A + 15A + 25A = 55A. 125% of 55A = 68.75A. So I will use minimum 70A breakers for the feeders; -OR-

if I use three 15A heaters (125% of 45A = 56.25A), I will use minimum 60A breakers for the feeders.

As far as what size feeder conductors go with various size breakers at the main panel -- per the third CU column in NEC Table 310.16, I believe required wire sizes, maximum continuous current, and allowed conbinations of heaters are as follows:

main breaker.....wire size.....max.cont.amps..........heater combos
60A.....#6.....48A..........would handle three 15A heaters
70A.....#6.....56A..........would handle two 15A plus one 25A -OR- two 25A heaters
80A.....#4.....64A..........
90A.....#4.....72A..........would handle three 15A plus one 25A heaters
100A.....#3.....80A..........
125A.....#2.....100A..........would handle three 15A plus two 25A heaters

What sizes I use may depend on what is available and at what cost.
How am I doing so far?

With many thanks,
Daneel
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Old 05-11-2011, 07:37 AM   #7
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Sub-panel for 3 space heaters


Daneel - reading posts is a great use of time tons of great information in them-there-threads.
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Old 05-11-2011, 08:52 AM   #8
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Sub-panel for 3 space heaters


I have a question I hope you will answer. What is the watt rating of the three heaters?
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Old 05-11-2011, 10:06 AM   #9
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Hi a7ecorsair,

Heater sizes...
Small ones (15A) are 3600 Watts.
Large ones (25A) are 6000 Watts.

3x 3600 Watt units and 2x 6000 Watt units are available.

Daneel
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Old 05-11-2011, 10:10 AM   #10
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Thanks, I was just wondering if the 15A was the required circuit size or the rated draw.
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Old 05-11-2011, 02:52 PM   #11
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Quote:
Originally Posted by Daneel View Post
Hi a7ecorsair,

Heater sizes...
Small ones (15A) are 3600 Watts.
Large ones (25A) are 6000 Watts.

3x 3600 Watt units and 2x 6000 Watt units are available.

Daneel
6,000 watts for each large baseboard heater or combined both heaters?

And are you going to use the thermosat in the baseboard heater or go with line voltage wall thermosat if latter you really have to watch the wattage rating otherwise may have to set up a relay box next to the breaker box so it can handle large heater without issue due most of the line voltage wall thermostat are genrally rated for 22 amp and make sure you get double pole verison.

I will reply more details later on the moring { it is nite time now in Paris France }

Merci.
Marc
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Old 05-11-2011, 04:03 PM   #12
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Sub-panel for 3 space heaters


Daneel, I just wanted to throw in my 2c for your [Q7].

I use these, and they're great for stripping the sheathing and the insulation on NM-B:

http://www.homedepot.com/h_d1/N-5yc1...atalogId=10053

Edit: Those will strip #14 and #12 (and #10 with some finesse), but it looks like those will be the least-used sizes on your project.

Last edited by ScottR; 05-11-2011 at 04:06 PM.
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Old 05-11-2011, 05:55 PM   #13
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Sub-panel for 3 space heaters


Hi ScottR,

Most work is with 14, 12 and 10. I am heading to HD next week and will check this tool out.

Thanks for the tip.
Daneel


Bonsoir frenchee,

By all means please get your beauty rest. Recevez sans doute s'il vous plaît votre reste de beauté.

These are not baseboard heaters. I'd call them insulated cabinet heaters - about 28" high. Individual heater power consumption is 3.6 kW or 6.0 kW. Each heater is filled with "fire brick" which stores beaucoup de BTUs and weighs several hundred kilos. Inside temperatures can reach over 600 Deg. C. Each heater has three circuit inputs:

(a) Power to the heating element circuit is always on, but not always heating the fire brick. See (c)

(b) Power to the fan (low current) circuit is always on, but one leg is in series with a wall-mounted line thermostat.

(c) There is a separate control panel that monitors outside temperature and the status of cheap "off-peak" electricity. The control circuit enables heating element(s) in all heaters simultaneously, but only when off-peak power is on and only for a period of time based on the outside temperature. Off-peak power is less than half of the cost of normal power, but the power company determines when it is available. These heaters store up BTUs at night. The fans blow out hot air anytime, depending on the setting of the thermostat for that zone.

Merci,
Daneel
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Old 05-11-2011, 09:47 PM   #14
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Sub-panel for 3 space heaters


Have you got a link for the heaters? I'd be interested in seeing what you are going to use.
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Old 05-12-2011, 12:12 AM   #15
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Sub-panel for 3 space heaters


Bonjour Daneel.,

Ahh Oui., Je sais qu'un très bien { I know that one very well }

We have couple of them in France as well due we use the Nuit { Nite } rates as well.

Ok you will have to sized to the max wattage of that heaters you have them and make sure you slect the conductor larger than you normally do due they are contionous opertiong { more than 3 Heures ( Hours )}

And make sure you follow the manufacter instruction for mounting and set up the heater very carefull.

Also check your floor stucture if need addtional bracing as well due that heater weight more than few hundreds Kilograms.

The last one I work on was weight in little over 450 KG so you can understand why you have to be carefull with it.

Merci,
Marc

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