Where's My Neutral?

[bishopthomas]

I have a gig coming up where we are trying to use the generators built in to the lighting towers. You've all seen the ones I'm talking about, they're tow-behind, has a crank up tower with 2/4 halogens (halide). There's one Edison circuit and one L6-30 circuit that I'm trying to make use of. The problem is that the L6-30 has no neutral (hot/hot/ground). So I'm wondering if I can share the neutral from the Edison. What I'm thinking is I could create an Edison breakout box that I would plug my gear into. The other end of the box would have one cable running to the Edison, the other to the L6-30. Inside the box is where I would simply jump from the Edison's neutral over to the feed from the L6-30. Any reason why this wouldn't work? Am I being clear about my wiring plan? Ultimately I would end up with 3 circuits. which is what I need. The only other option would be to rent a separate generator but we're trying to avoid that.

 

[Footer]

You have a few issues here... legalities aside. Biggest thing is overloading your neutral. Depending on how the circuits are wired you could really be overloading your neutral. If each of your hots are on a different phase then you SHOULD be ok. If the edison shares a leg with anything on the L6-30 then you are SOL. Your other issue is the edison is breakered for 15 or 20 amps. The L6-30 is breakered for 30 amps. So, the neutral you have is wired for 20 amps. By hooking it up to a 30 amp breaker you run the risk of roasting that neutral once again. You are you SOL. Rent a proper generator and get the right power.

 

[JD]

Have to agree with above. Last time I had one apart, the lamp ballasts were all 230 volt. Like many small portables, the neutral was strapped to the frame inside the generator head itself. Although the two hots are of gauge, chances are that the Edison is fed with whatever wire gauge is appropriate for what its protected at.
Despite the Edison, consider this unit to be a 230 volt only generator.

 

[bishopthomas]

How is the neutral wired for 20A? Most panels have a bus bar for the neutrals, so there's 100+ amps going across the neutrals. They're not breakered so how can a neutral be rated (besides cable capacity)?

 

[bishopthomas]

Here are a couple of pictures I took. You're right, JD, neutral is attached to the frame.

 

[bishopthomas]

Okay, so we're renting generators. But I'd love to keep this conversation going for my own info/knowledge. I run into this situation from time to time and it would be nice to know if this is possible in a pinch.

 

[Footer]

How is the neutral wired for 20A? Most panels have a bus bar for the neutrals, so there's 100+ amps going across the neutrals. They're not breakered so how can a neutral be rated (besides cable capacity)?

Cable capacity is exactly it. Odds are that neutral is 12 gauge wire. If you opened it up and connected a L14-30 and ran the neutral to the buss bar you would be all set.

 

[JD]

Cable capacity is exactly it. Odds are that neutral is 12 gauge wire. If you opened it up and connected a L14-30 and ran the neutral to the buss bar you would be all set.

What Kyle said.
For the hypothetical discussion I would add two other things:
1) You would want to double check the actual neutral wire size coming from the generator head. No reason to not think it would be correct, but you would want to check.
2) Your original post contained a flaw brought out by the picture- The Edison is a CGIF (ground fault protected.) If you had used it to grab a neutral, it would have sensed the imbalance and tripped, possibly* leaving you without a neutral connection!

In any case, rewiring the generator would open a whole new can of legal worms! (and nullified any UL or other rating.)

*Must say, the GFIs I've taken apart only interrupt the hot, not sure if the CGIFs also interrupt the neutral as well.

 

[Billincie]

What about a break-out box where you power 2 of the 3 120v. lamps in series on the 240v. twist ?.... Assuming they are the same wattage lamp.

 

[n1ist]

Unplugging the 5-15 on that adapter box while things are running would both blow up your loads (if they weren't equal resistance) and would give you a hot male pin (illegal and potentially deadly).
/mike

 

[PeteEngel]

You bring up a good point about the GFCI. It should interrupt the hot, but the toroid in the GFCI is (should be) around both the Hot and Neutral legs to make sure the same amount of power going out is coming back. Any variable is read as a ground fault and the GFCI trips. If you tie another neutral to the original, the neutral will read more voltage than the hot under operation and theoretically should trip. Something to think about.

 

[avkid]

I have a gig coming up where we are trying to use the generators built in to the lighting towers. You've all seen the ones I'm talking about, they're tow-behind, has a crank up tower with 2/4 halogens (halide). There's one Edison circuit and one L6-30 circuit that I'm trying to make use of. The problem is that the L6-30 has no neutral (hot/hot/ground). So I'm wondering if I can share the neutral from the Edison. What I'm thinking is I could create an Edison breakout box that I would plug my gear into. The other end of the box would have one cable running to the Edison, the other to the L6-30. Inside the box is where I would simply jump from the Edison's neutral over to the feed from the L6-30. Any reason why this wouldn't work? Am I being clear about my wiring plan? Ultimately I would end up with 3 circuits. which is what I need. The only other option would be to rent a separate generator but we're trying to avoid that.

We use them all the time, it's simple:
FOR QUALIFIED PERSONNEL ONLY
Remove the front panel screws and open the panel
Disconnect the spades on both the outlets (6-30 and 5-15)
Isolate the 5-15 hot and neutral (wire nuts or block)
Run a a new neutral from the neutral bus bar
Join the hots to your cable (bare end with a nut or a terminal block and spade connectors)
Thoroughly encase the terminal block(s) in rubber electrical tape
Ground with copper rod, clamp and something to attach to the trailer frame
Meter to make sure everything is correct

Once you do this your cable can exit out the existing chase that goes under the generator and the panel can be closed to appear normal.
Zero risk of anyone doing something stupid once it is closed as neither outlet works.
As long as the equipment is restored at the end of the gig the rental companies don't care, United Rentals has actually given us permission to do this after explaining it to a service tech.