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Old 09-26-2007, 11:53 PM   #16
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12/3 Romex to Feed 2 Circuits?


Hi Andy

I see you work with a lot of three phase . One thing, if our not already aware, is for your 4 wire wye connected loads that are non-linear....for instance many plants have lighting panelboards that supply ballasted lighting loads. Be very careful doing multiwires out of these as there is a good chance of harmonics overloading a normally sized shared neutral, especially shared with all 3 phases. It's a very good idea to run a neutral for each phase in these situations or up size your shared neutral to prevent the "triplen" effect from the lighting loads. In specific your panels supplied by 4 wire wye 227/480 and 120/208 are especially susceptible to these non-linear load harmonics. So if not up to speed take a look at this it is a growing problem and a lot of commercial building fires have been attributed to the heating of overloaded neutrals in these situations.

Stubbie

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Old 09-27-2007, 12:09 AM   #17
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12/3 Romex to Feed 2 Circuits?


Once a while i will get the service call from the commercal / industrail loaction when anytime i heard someone smoked something i say they [unqalifed mantanice guys ] mess around with it that true with MWBC it dont matter which votlage ya run on it once you " lift " the netural ya are screwed.

one place have MWBC for lumiaire circuits this place the MWBC i rather say pretty hevey loaded large number of 1 KW HPS lumniaires [ each were wired for 277v ] and somehow one idiot did cut the wrong neutral at the lighting panel jezz what a firework show. next thing they called me to come in and try to repairs all the mess i just say tons of french [ i cant even type french cussing words in here also lol ] total lumniaires were 30 of them on one MWBC and ya know what the cost of 1 KW HPS high bay were all the ballast just smoked in 15 seconds flat and left part of the building in dark.

anyway before i get out of the hand in here let get back to the subject what stubbie just say few second ago about the harmomic issuse this will show up not only in electronic ballasted lumiaires but also with other electronic equmient i know one place have computers and they did really a wonderfull work on the netural wires that place have 600 amp service the netural wire just burnt the heck out of it and have to oversized it and paralled it to slove the issuse there

sorry for long thread there

Merci , Marc
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Old 09-27-2007, 12:41 AM   #18
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12/3 Romex to Feed 2 Circuits?


Marc......Did you ever forget to let the bulb cool before you unscrewed it....let me tell ya they are very freakin hot......

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Old 09-27-2007, 12:54 AM   #19
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12/3 Romex to Feed 2 Circuits?


Subbie,, yeah i was well aware with the HPS and MH bulbs are freaking hot but tell ya one instering part i did used hevey welding gloves and i unscrew the 400 hps and it was still lit for about 40 seconds after i took it out of the base.

the new guy was working with me he went like this >>

but one thing Stubbie. Never fool around with MH bulbs when still hot i have few expoled on me. i have scar to prove it from that freaking bulb blew up on me [ that happend right after i open the hevey glass door on wall pack next thing i heard crack then i was pushed back a sec. i knew what it did a good size drop of water from the gutter drop down and make a nice target at the hot bulb and exploled ]

i think we better get back on track here other wise why not start the seprated thread so it dont confused with the OP and other wondering why we are at this >>

Merci, Marc
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Old 09-27-2007, 07:53 AM   #20
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12/3 Romex to Feed 2 Circuits?


I won't disagree on the MWBC issue. I feel better using a separate line for each breaker.

As for the #14 VS #12 issue, I don't know where I read or heard this. I will have to check the local code.
It definitely makes sense to use a 20A breaker for #12 wire. Makes the job much easier if you can get away with fewer circuits. Only issue would be that you need to make sure the whole circuit uses #12 (at least for receptacles).

The house I am currently living in (my parents home) is 80 years old, and has a lot of the old rubber/cloth BX, and possibly some knob & tube, but so far I haven't seen any of the latter.
We all know the house is in need of rewiring, but it is a job beyond my current capabilities. I'm OK with the wiring part, but having to get the wires to where I want them is something I would rather leave for someone else <g>

FW
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Old 09-27-2007, 10:02 AM   #21
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12/3 Romex to Feed 2 Circuits?


Quote:
Only issue would be that you need to make sure the whole circuit uses #12 (at least for receptacles).
Cross out your qualifier at the end and you would be 100% correct.

If the breaker is 20A, you MUST use #12 conductor throughout the entire circuit**, lighting AND receptacles.

**There are exceptions to this, but none of them apply to "normal" lighting/receptacle circuits.
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Old 09-27-2007, 03:16 PM   #22
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12/3 Romex to Feed 2 Circuits?


Quote:
Originally Posted by Stubbie View Post
Hi Andy

I see you work with a lot of three phase . One thing, if our not already aware, is for your 4 wire wye connected loads that are non-linear....for instance many plants have lighting panelboards that supply ballasted lighting loads. Be very careful doing multiwires out of these as there is a good chance of harmonics overloading a normally sized shared neutral, especially shared with all 3 phases. It's a very good idea to run a neutral for each phase in these situations or up size your shared neutral to prevent the "triplen" effect from the lighting loads. In specific your panels supplied by 4 wire wye 227/480 and 120/208 are especially susceptible to these non-linear load harmonics. So if not up to speed take a look at this it is a growing problem and a lot of commercial building fires have been attributed to the heating of overloaded neutrals in these situations.

Stubbie

I hear ya stubbie!! Most of our work is speced out by lighting engineers with upgraded neutrals where triplen harmonics will be a problem. It took a while after coming out of roping houses for harmonics to click...but when the lite bulb came on it came on bright pun intended...
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Old 09-28-2007, 08:24 AM   #23
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12/3 Romex to Feed 2 Circuits?


My local building inspector just replied to an e-mail I sent on the subject of wire size for branch circuits;
#14 is OK for 15A circuits.
I don't know where I got the erroneous info.

Perhaps I got into the practice of using #12 on 15A lines when we still had the Federal Pacific breakers. They were so lousy, I had tested some of the 15A and they would not trip at 19A even after 1 hour. AT 25A, the 15A breaker took about 20 minutes to trip out!
I had a guy from the power company tell me that those breakers were dangerous! Yet I still see FP around today.
We have since replaced the panel with CH, which IMO are the best breakers on the market.

FW

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