sub panel

[finster1]

I love all the hype subpanels create, but I've had this arguement before and I believe it is clear. If I was to run a subpanel in say a basement(indoors, for arguement sake) in conduit lets say 1" emt. The proper size wire for a 240v single phase 100A service would be (3) #3 thhn 2 HOTS A NEUTRAL and I prefer to run a seperate ground even though my hypothetical senario is emt and it is not necessary. I feel the seperate ground, ends the need for bonding bushings at the concentric fittings usually found at the panel knockouts. I mention all these things because I've sat around and argued with my collegues on almost all the things I've mentioned from concentric knockouts requiring a bonding bushing, to the size of the wire to actually be allowed for a 100 amp panel, to the need or lack of a ground if you are using emt. #3 thhn should clearly be the choice for 100....I see #4 all the time and technically I feel it shouldn't be allowed to be protected by a 100a breaker.Also another issue I have and I am not sure where it is addressed, can we use aluminum wiring for a subpanel in an indoor area.... Here in NJ the insurance companies really frown on aluminum except as a service wire for the main panel.....a sub is technically not that, so why do I find it installed even in recent applications indoors??? OK enuff said...any feelings guys?

Jim P
Licensed Electrical Contractor NJ

 

[wbalsam1]

I love all the hype subpanels create, but I've had this arguement before and I believe it is clear. If I was to run a subpanel in say a basement(indoors, for arguement sake) in conduit lets say 1" emt. The proper size wire for a 240v single phase 100A service would be (3) #3 thhn 2 HOTS A NEUTRAL and I prefer to run a seperate ground even though my hypothetical senario is emt and it is not necessary. I feel the seperate ground, ends the need for bonding bushings at the concentric fittings usually found at the panel knockouts. I mention all these things because I've sat around and argued with my collegues on almost all the things I've mentioned from concentric knockouts requiring a bonding bushing, to the size of the wire to actually be allowed for a 100 amp panel, to the need or lack of a ground if you are using emt. #3 thhn should clearly be the choice for 100....I see #4 all the time and technically I feel it shouldn't be allowed to be protected by a 100a breaker.Also another issue I have and I am not sure where it is addressed, can we use aluminum wiring for a subpanel in an indoor area.... Here in NJ the insurance companies really frown on aluminum except as a service wire for the main panel.....a sub is technically not that, so why do I find it installed even in recent applications indoors??? OK enuff said...any feelings guys?

Jim P
Licensed Electrical Contractor NJ

250.92(B) (bonding around concentrics) does not apply to remote panelboards with feeders, only service conductors. Aluminum is permitted for indoor remote panelboards by the NEC. Check your local restrictions, if any. :smile:

 

[celtic]

Here in NJ the insurance companies really frown on aluminum except as a service wire for the main panel.....a sub is technically not that, so why do I find it installed even in recent applications indoors??? OK enuff said...any feelings guys?

Who cares if the insurance company frowns...AL is legal....if the ins. co.s don't like that fact, they ought to write a proposal to ban it's use.

FWIW...all the panels at the new Devil's Arena are feed with......ALUMINUM.


You will continue to find AL feeding subs until AL is banned for that use.

 

[winnie]

Wow. Lots of issue density in that post!

1) I agree that in general, for a subpanel, you cannot use 310.15(b)(6) to size the conductors. If the feeder to the subpanel constitutes the _main_ power feed to a residence, or if the feeder to the subpanel has the same amp rating as the main power feed, then I belive that you can use 310.15(b)(6) to size these conductors. (Examples, if you have a 'meter main' outside, and then a feeder to a panel that carries the whole of the load of the residence, then 310.15(b)(6) is good for sizing. Second, if you had say a 100A service, with conductors sized using 310.15(b)(6), and then have a subpanel with a 100A feeder, then the feeder conductors would not need to be larger than the service conductors.)

2) If proper conductor termination procedure is followed, no problems with aluminium feeders.

3) Thumbs up on the _preference_ for a separate EGC. But note that an _intact_ conduit system has lower resistance than the EGC that it contains; if a particular situation requires a bonding bushing, I don't see how having that EGC eliminates the requirement.

-Jon

 

[cadpoint]

Always Interesting ...

Always Interesting ...

I love all the hype subpanels create, but I've had this arguement before and I believe it is clear

The term, "Subpanel" doesn't exist in the NFPA-70 (2005), I understand the hype

You might look at 250.86, this is a cross refenerenced from 250.110(5) but truely (6) well it is over 150 V to ground.

250.112 also seems to apply. But you didn't say how the conduit got there
so exceptions come into play because you didn't state it , Don't know.

If I was to run a subpanel in say a basement(indoors, for arguement sake) in conduit lets say 1" emt. The proper size wire for a 240v single phase 100A service would be (3) #3 thhn 2 HOTS A NEUTRAL and I prefer to run a seperate ground even though my hypothetical senario is emt and it is not necessary. I feel the seperate ground, ends the need for bonding bushings at the concentric fittings usually found at the panel knockouts.

...

...I see #4 all the time and technically I feel it shouldn't be allowed to be protected by a 100a breaker.

So your going to write a proposal for 2011! Good Going !

.....a sub is technically not that, so why do I find it installed even in recent applications indoors??? OK enuff said...any feelings guys?

 

[kbsparky]

You can use a #4 for the neutral (even smaller, if your load calcs permit it). No need to waste resources on that #3 for anything other than the hots.

 

[iwire]

Wow. Lots of issue density in that post!

LOL. Never heard it put that way but yes there was.

 

[infinity]

You are incorrect in stating that bonding around concentric or eccentric KO's is required for a 240 volt subpanel. You certainly can use them but they are not required.

I mention all these things because I've sat around and argued with my colleagues on almost all the things I've mentioned from concentric knockouts requiring a bonding bushing, to the size of the wire to actually be allowed for a 100 amp panel