Panelboard & Subpanel Question

Status
Not open for further replies.

ote

Member
Location
NC
I'm pricing up a single family residence, 2 story, 3000sq feet. HO has plans with double ovens, range, DW, seperate heat & ac for each floor, exterior hot tub, well pump. I did load calc. and came up with 176 amps. Panel location shown is on interior mech rm of house, so I'm figuring exterior 200a disc and 4 wire feed to panel. My question is, after looking at plans and figuring circuits needed, I need total of 51 breaker spaces. 200amp panel has 40 spaces and was figuring adding subpanel next to main breaker panel to allow for additional circuits. Anything wrong with this code wise? Don't know what else to do in this situation. I could add an additional subpanel just for the second floor, but not enough circuits up there (1000 sq ft) to ease circuits in main panel. Anybody ran into this before?
 

lakee911

Senior Member
Location
Columbus, OH
When you do that, how do you the handle grounding issues if ground is bonded to nuetral in first panel? Still requires seperation in second panel?
 

jrohe

Senior Member
Location
Omaha, NE
Occupation
Professional Engineer
When you do that, how do you the handle grounding issues if ground is bonded to nuetral in first panel? Still requires seperation in second panel?

The bond would be in the exterior disco, not the first panel.
 

busman

Senior Member
Location
Northern Virginia
Occupation
Master Electrician / Electrical Engineer
I'm not sure the code is 100% clear on that, but I've assumed that since the main OCPD is in the first panel, it's only bonded there and I've run 4 wires to the second panel and kept ground/neutrals separate. Always passed inspections.

Mark
 

lakee911

Senior Member
Location
Columbus, OH
The bond would be in the exterior disco, not the first panel.

I know that in this case, but I did say "if ground is bonded to nuetral in first panel." :D

I'm not sure the code is 100% clear on that, but I've assumed that since the main OCPD is in the first panel, it's only bonded there and I've run 4 wires to the second panel and kept ground/neutrals separate. Always passed inspections.

That's what I'd assume (to be safe), but one could argue that extending the three busses wouldn't really change anything either...
 

ZZDoug

Member
Location
North Dakota
I'm not sure the code is 100% clear on that

Its very clear. You bond ONLY ONCE anywhere between the source (usually a transformer) and first disconnect, and never downstream after that. If more electricians would learn the reason why instead of just memorizing the rules, this would be easier to understand. There is an exception in the code allowing for more than one connection, but its still between the source and disconnect only, and its rarely applicable.
 

busman

Senior Member
Location
Northern Virginia
Occupation
Master Electrician / Electrical Engineer
Its very clear. You bond ONLY ONCE anywhere between the source (usually a transformer) and first disconnect, and never downstream after that. If more electricians would learn the reason why instead of just memorizing the rules, this would be easier to understand. There is an exception in the code allowing for more than one connection, but its still between the source and disconnect only, and its rarely applicable.

I do understand the reason for it, but the code says:

"including the terminal or bus to which the grounded service conductor is connected at the service disconnecting means".

I think it would be more clear if it said, "inside the enclosure containing the service disconnecting means". If the ungrounded conductor is run thru a lug in the first panel and is continuous to the lug in the second panel, then the conductor is connected to more than one bus and I would argue that you could connect the MBJ to either bus or put one in each panel (as you do when there are multiple disconnects). It's not that I don't clearly understand the intent or the reason, I just don't think the wording is completely clear.

Mark
 

ZZDoug

Member
Location
North Dakota
Mark, you have me confused a bit here. The phrase you are quoting is from 250.24(A)(1). That is referring to the GEC and service neutral connection. What it is saying is the connection can be made anywhere from the service drop or lateral to the terminal in the service panel. This is essentially the same thing as 250.30 says (anywhere between the source and first disco) about the connection between the grounded conductor (neutral) and equipment ground, which of course is almost always done at the same point. Just as an aside you will run across many electricians who think this connection must be made in the meter can, beware inspectors who insist on this. Anyway I dont see what isnt clear. Both of these passages are saying the same thing.

But then you said "If the ungrounded conductor is run thru a lug in the first panel and is continuous to the lug in the second panel". What you are describing now is a sub-feed lug and not the feed-thru lugs you were talking about before. Using sub feed lugs would require OC protection somewhere upstream from both panels, meaning you would have to bond at that OC location and therefore neither panel. But with feed-thru lugs the second panel would be fed from the first panels main breaker, making the second panel a sub panel. And you never bond in a sub panel which is as I described before as "downstream". You bond anywhere between the source and first disconnect, which for a regular home is the main breaker in the service panel. What isnt clear?

I can see your confusion about the multiple disconnect situation though, but remember that each of those are SERVICE disconnects. Service equipment is not the same as a subpanel at all.
 
Status
Not open for further replies.
Top