Lighting Panelboards

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mkctnm4

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I have a SQD, 42 cicuit, 225A,MB lighting panelboard feeding a second SQD, 42 circuit, 225A, MLO panelboard. It is a parallel feed to the second panelboard from the first. The panelboards have two 2.5"x12" EMT conduit connecting the two. One of these is used for the feeders going to the second panelboard.

The MB panelboard has a 4-wire system with grounding electrode conductor. The second panelboard only has a 4-wire with no grounding electrode, equipment grounding conductor, or bonding conductor from the first panelboard.

My question is that I believe this second panelboard is not a sub-panel, merely an extension of the first panelboard providing 84 circuits for lighting and appliances. I also believe that the grounding electrode conductor needs to be taken to the second panleboard and that the raceway should be bonded on both sides with a bonding locknut.

My problem is that if this is all true, I cannot find the code that relates to this if it has to be done or not.

Any help would be greatly appreciated.
 
Is the main breaker panelboard the service disconnect? As in, do the conductors supplying that panel come from the utility?

If not, then the Grounding Electrode Conductor should not be in this panel anyway. 250.24(A)(1).

I'm curious about the conductors supplying the main breaker panel, as well as the one supplying the MLO, and how those conductors are terminated inside the MDP. Can you provide those details?

You've used the term "parallel" which calls to mind different things for different people, I'd like to get an accurate picture inside my head about what you mean. :)
 
RE: Lighting Panelboards

The MB panelboard is the service disconnect for both panelboards. The lugs in the MB panelboard are a double lug system. The utility feed comes into the MB panelboard then feeds the second. The panelboard with the MB is a SQD CAT#12208167280340001 and the second panelboard is a MLO SQD CAT#12208167281040001.

Hope this helps.

Thanks
 
mkctnm4 said:
I believe this second panel board is not a sub-panel, merely an extension of the first panelboard providing 84 circuits for lighting and appliances.
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It is two separate panel boards regardless of how they are suppled.

Check the definition of panel board in Article 100.

Those two individual panel boards where not 'designed to be assembled into a single panel.

If you did call these 'one panel board' you would be limited to 42 over current devices. 408.35
 
Thanks for the pictures! :cool:
mkctnm4 said:
The MB panelboard has a 4-wire system with grounding electrode conductor.
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How does the grounding electrode conductor get into that conduit with the service conductors?

Both ends of ferrous conduits containing a GEC are required to be bonded at both ends, 250.64(E).

The second panelboard only has a 4-wire with no ... equipment grounding conductor ... from the first panelboard.
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The EMT between the panelboards is a EGC per 250.118.

I also believe that the grounding electrode conductor needs to be taken to the second panleboard and that the raceway should be bonded on both sides with a bonding locknut.
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Not necessary. 250.24(A)(1) requires it to be brought to any accessible point up to (and including) the service disconnect. If the GEC is brought to the first panel and terminated, the NEC is satisfied.
 
BTW this is very common in office building where we have a ton of circuits with little load each.

A lot of times we install a 400 amp feeder to a group of 3 feed through panels.
 
I understand the definition of a panelboard. However it appears that the second section is being treated as a sub-panel with the grounded conductor being isolated. This is a 400 amp service. I don't know that I would want to rely on a 2.5"x12" piece of metal for grounding purposes.

So if I am understanding the correctly is that the grounding electrode conductor from section one does not need to go to section two and the the 2.5"x12" nipples do not need to be bonded? The installation is fine as it sits?

I appreciate everyones input...Thanks
 
mkctnm4 said:
I understand the definition of a panelboard. However it appears that the second section is being treated as a sub-panel with the grounded conductor being isolated.
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That is correct.

This is a 400 amp service. I don't know that I would want to rely on a 2.5"x12" piece of metal for grounding purposes.
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Why not? The connection to earth at the second panel is of marginal consequence.

The nipple will be used for conducting ground fault current, it's unlikely a lightning bolt is going to hit the second panel. :)

Edit: I would install an Equipment Grounding Conductor between the two panel's grounding bars, myself, but it is not required.

So if I am understanding the correctly is that the grounding electrode conductor from section one does not need to go to section two and the the 2.5"x12" nipples do not need to be bonded? The installation is fine as it sits?
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From a grounding/bonding standpoint, yes. *

*I still don't know how your GEC is getting in with your service conductors.

However, the setup you have could be a violation of 408.36(A).

You keep saying that this is a 400A service, implying that the main breaker is 400A; but you said the first panelboard is a 225A panelboard.

All the current to the second panel is travelling through the first panelboard's busses to get to the feed-through lugs, and then on to the second panel. Therefore, when the second panel is at 200A, and your first panel is at 200A, the first panel's bus is conveying close to 400A.

If the breaker is a 200A breaker, then you are fine, but you have a 200A service.

Are the conductors 500 MCM? If so, is the load calculated at between 351 and 380 amps?
 
Is this really a service? I don't see where the GEC is located or terminated on the grounded conductor bus. IMO it's not a 400 amp anything. The conductors feeding the main CB appear to be #4/0 which would normally be used for a 225 amp panel. The feed through bus to the next panel section is a very common commercial installation.
 
mkctnm4,

Where is the main bonding jumper? It does not appear to be a wire or busbar installed from the grounded conductor bar to the equipment grounding bar. The GEC should land on the grounded conductor bar, rather than the equipment grounding bar. See 250.24(A)(1) and 250.24(A)(4)

Are you sure that is a GEC and not a bonding jumper coming form the meter?
 
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