Widowmaker Plug/clip

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hvac809

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Hey guys just looking for some clarification. I was working on a 240v condensing unit and needed 120v for a vacuum pump, but the nearest outlet was over 100' away and didn't want to burn up my pump. A co-worker suggested I make a widowmaker clip with the female end of an extension cord. He said put black(hot) under one of the line side contactor lugs and white and green under the ground terminal lug. I thought the only time ground and neutral were connected was at the panel? I also figured this would cause the chassis of the condenser to become live as the current carrying neutral was connected to it? He said if I check with my amp clamp I'll see no current on green but equal values on hot and neutral because current returns to the source? Is this the correct way to hook one of these clips up and is it even safe/legal? Why would no current be carried through the ground wire that's connected with the neutral? Thank you in advance for any input, I'm sure I'm overthinking it and misunderstanding the basic physics of electricity. ?
 
There is a reason such installations are called "widowmakers." Your instincts are serving you well. This is wrong, as you suspected. You are right in saying the ground and neutral should only be connected at the panel. You are right in saying that violating that rule will cause current to flow equally in both the neutral wire and the "equipment grounding path." That "path" includes the green wire and any metal that is bonded together (pipes, ducts, equipment enclosures, motor casings) and that lies between the inappropriate N-G bond point and the panel. Your co-worker is wrong in saying that the fact that current will return to its source (a true statement) means that it will only flow along the neutral (a false statement). Current will take any and all paths that it can find, any that lead back to its source. And yes, the green wires and the bonds between metal parts can be one of the available paths.
  • Step one: Don't do it.
  • Step two: Tell your co-worker that he is wrong. Feel free to give him a link to this discussion.
  • Step three: Ask your co-worker whether he has used this process before. If so, he needs to go back to every place he installed this thing, and (at his own personal cost, with no cost to the client) undo it, and make it right. This may require him to pay the costs (out of his own pocket) to hire electricians to make a safe installation.
 
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This thread was temporarily removed from the active forum, while the moderators discussed whether it is appropriate - given the unsafe practice that it discusses. We agreed that the OP is not asserting a desire to implement this unsafe practice - quite the opposite in fact. The OP is asking us to confirm his suspicions that the installation concept presented by his co-worker is neither safe nor code compliant. My post #2 provides my confirmation of the OP's views.

This thread is therefore being reopened. I apologize to the OP for the delay and inconvenience.
 
Electrically speaking, it would work, just like your own service where the bare conductor is also a current-carrying conductor. You would only energize the chassis to the extent of voltage drop along the EGC.

Having said that, your instincts are correct that it is a bad practice. It's certainly proper to use an EGC for testing voltages when a neutral is not present, but not as a current-carrying conductor, even temporarliy.

That's why code requires a receptacle for servicing HVAC equipment within 25' now. You need to use a portable generator, invest in a 100' 10g cord, or sell the job to install a receptacle and circuit for servicing.
 
Larry just woke me up to something I had missed. Your HVAC system is supposed to already have an outlet within 25 feet. So you are already in violation of that requirement. That outlet is not intended to be used for a permanently installed component, but rather for plugging in the tools you need to use while maintaining the system. I don't know whether the vacuum pump you mention is something that operates at the same time as the condensing unit, or is one of the tools related to servicing. But as long as you have something within 25 feet, it can be used in any way that it is needed.
 
By the way, there may be an easier and less expensive option for getting a closer receptacle, rather than running 100 feet of conduit and wire to extend the existing outlet to a second one closer to the HVAC system. But it would certainly require the participation of a qualified electrician. That person may be able to connect wires to the incoming 240 volt circuit, and use them to power a single phase step-down transformer. That in turn can be connected to a fused disconnect and a receptacle outlet. The main issue is whether there is a wall or other surface close by, giving you a place to mount these items.
 
Don't forget the SDS bonding and electrode requirements.

Let's see how convoluted we can make this. ;)
 
charlie b said:
Larry just woke me up to something I had missed. Your HVAC system is supposed to already have an outlet within 25 feet. So you are already in violation of that requirement.
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Depends on when the installation was installed. He didn’t say whether it was at a house, on a roof, etc. maybe it was installed before 1999...
rooftop later.
 
He said if I check with my amp clamp I'll see no current on green but equal values on hot and neutral because current returns to the source?
Click to expand...

Obviously not clamping the meter at the correct point in the circuit!:rant:

The current read on the hot wire to the widowmaker will equal the current on the ground wire that the white neutral from the widowmaker is connected to. Of course the green wire on the widowmaker will not read any current, it is out of the circuit!

I've seen way too many loose conduit connections to ever rely on one for a neutral return path. That is also why I always run a real ground wire in conduit.
 
When I was young, I discovered the hard way that (what I discovered was) an unterminated EMT sleeve is not a reliable neutral.
 
Your vacuum pump may be able to run off of 240V directly, if the motor leads are accessible and it's just a pump, no controls or electronics.
 
Luckily some HVAC service companies frown upon using a bootleg neutral to power vacuum pumps, & recovery machines, when only 240V is available.
 
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