Generator in a outside building and powering the panel...

[aczlan]

700.19 Multiwire Branch Circuits Prohibited

A new 700.19 has been added addressing multiwire branch circuits used in emergency systems. This new provision prohibits multiwire branch circuits protected by common trip circuit breakers to serve emergency lighting and power circuits. Emergency lighting and power could be unavailable during ordinary line to ground faults and other problems where common trip circuit breakers or handle ties are employed. Continued reliability of emergency circuits requires this change. [ROP 13-118]

Are you sure that applies? I looked at that section last night and as I understand it, that section only applies to things like emergency lighting that are considered critical to life and health. This genset would be classed as an optional backup genset (702.9) rather than an emergency system.

Aaron Z

 

[MossRoad]

Are you sure that applies? I looked at that section last night and as I understand it, that section only applies to things like emergency lighting that are considered critical to life and health. This genset would be classed as an optional backup genset (702.9) rather than an emergency system.

Aaron Z

Here's a link to a nice booklet that explains it all.... ANnnnnddd.... It looks like you're good to go.

http://www.google.com/url?sa=t&rct=...E-kvNQssECVnvrZzf4OLq4g&bvm=bv.77880786,d.aWw

 

[GPintheMitten]

Are you sure that applies? I looked at that section last night and as I understand it, that section only applies to things like emergency lighting that are considered critical to life and health. This genset would be classed as an optional backup genset (702.9) rather than an emergency system.

Aaron Z

I agree Aaron. That section is for emergency power like at hospitals exit lighting at public places like theaters etc.

Your situation is optional backup power.

 

[CobyRupert]

Geesh! I'm on the side that says he can do it, but Lord Mercy, let me offer those who say he can't some fodder, cause ya'all need some help: Argue this: Article 300.3 (B). So when running genny power, where is the neutral conductor for subpanel neutral current now? (I'm making a better argument for your side and I don't even agree with myself! :laughing: :confused2

 

[buickanddeere]

I'm going to have to eat 1/2 a crow here . While drawing out the wiring plan with the existing conductors and using a Kirk-key on the generator breaker and a Kirk-key at the house 200amp main breaker for the electrical Code Inspector this morning. Well darn, I realized that I missed something . It is legal.
The plan B however to pull generator powered conductors into the same conduit as the regular supply to the barn. This made the Inspector growl and say no d@mmed way.

 

[aczlan]

I'm going to have to eat 1/2 a crow here . While drawing out the wiring plan with the existing conductors and using a Kirk-key on the generator breaker and a Kirk-key at the house 200amp main breaker for the electrical Code Inspector this morning. Well darn, I realized that I missed something . It is legal.

Good to know, might have to look into prices on one of those.

The plan B however to pull generator powered conductors into the same conduit as the regular supply to the barn. This made the Inspector growl and say no d@mmed way.

Can you (or the inspector) elaborate on what section of the NEC forbids it (assuming that it is not a separately derived system and as such, the neutral and ground are always connected to both the generator and the mains power)?
It would seem that this would be classed as an optional standby system and fall under 702.9 which states the following:

702.9 Wiring Optional Standby Systems. The optional standby system wiring shall be permitted to occupy the same raceways, cables, boxes, and cabinets with other general wiring.

Thanks

Aaron Z

 

[buickanddeere]

Becomes a separately derived source in the same conduit so it's not considered safe or legal.

 

[aczlan]

Becomes a separately derived source in the same conduit so it's not considered safe or legal.

Can you explain why that is?
Everything I have read says that if the neutrals and grounds are unbonded at the generator and then run separately to the main panel (where the generator neutral is then bonded to the system neutral and the generator ground is bonded to the system ground) it is NOT considered a separately derived system and only the 2 hots from the generator need to be switched.
If the neutral and ground were bonded at the genset and switched with the hots in a transfer switch before the main panel, yes it would be a separately derived system, but that is not what is being discussed here.

Aaron Z

 

[buickanddeere]

It's where they draw the line with the code as the exemptions become too complex.
The Inspector was not concerned about sharing the neutral or the ground.
It all revolved around the definition of two sources in the same conduit. Which can occur if the gen set is operating and energizing the wires up to the breaker at the 200amp panel even though the generator breaker is still locked open at the 200amp panel. It's due to cable insulation faults in conduit, in particular underground conduit. Now the generator and utility can cross connect via the short.
There are a number of incidents commented on this site about underground cables going" Ka-Pow" due to time and environment. So the concern is real.

 

[GPintheMitten]

It's where they draw the line with the code as the exemptions become too complex.
The Inspector was not concerned about sharing the neutral or the ground.
It all revolved around the definition of two sources in the same conduit. Which can occur if the gen set is operating and energizing the wires up to the breaker at the 200amp panel even though the generator breaker is still locked open at the 200amp panel. It's due to cable insulation faults in conduit, in particular underground conduit. Now the generator and utility can cross connect via the short.
There are a number of incidents commented on this site about underground cables going" Ka-Pow" due to time and environment. So the concern is real.

Is the inspector allowed to overrule this?


702.9 Wiring Optional Standby Systems. The optional standby system wiring shall be permitted to occupy the same raceways, cables, boxes, and cabinets with other general wiring.