Bonding can with neutral

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wawireguy

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So I'm doing a case study on a project we are doing at work just for my own enjoyment.

We are bringing a 400amp 120/208 feeder into a can from a overhead drop with no EGC. From that can we are tapping to two 200amp panels. Should the can be bonded to the neutral? This is a outside temp FYI. We are using PVC conduit for the taps to the sub panels.

Now what if we had went with EMT conduit? The can would be bonded to the sub panels.

I decided the no ground with the feeders was fine, 250.32(B)
Also decided the taps were alright, 240.21(B)(5)

Can't find where it discusses bonding that can though. I know it needs to be bonded to the grounded conductor but want to see the code reference.
 
If you're in WA, you should be using the 2008 code and there is a WAC rule mandating 4 wire feeders to detached buildings so you can't use 250.32 (B). But I don't think you're describing a feeder. The wires to and from the meter can are usually Service Entrance Conductors. So the two 200A panels are your main disconnect.

Everything on the line side of the service disconnect (i.e. the meter can) is permitted to be bonded by the grounded conductor [250.142(A)]. You also can not use EMT for Service raceways in WA. And you need to follow all the Service Bonding rules on the can if the service drop comes in via a metal conduit (most likely a bonding bushing unless you've got a hub connector on the meter).

Every piece of metal has to be bonded. I don't know if you'll find a meter can that isn't well bonded to the neutral/grounded lug in that can.

Now if this really was a feeder from your own overhead distribution and not utility service conductors, and you're installing your own meter, then this is a whole different situation. If so, see 250.142(B) Exception 2.
 
It's a feeder and not a service with a meter. I'll get back to this later tonight I'm thinking. It is a very interesting install to me. Triplex overhead. Unlimited outdoor taps to sub panels.
 
wawireguy said:
So I'm doing a case study on a project we are doing at work just for my own enjoyment.

We are bringing a 400amp 120/208 feeder into a can from a overhead drop with no EGC...
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At a glance it seems fine, if your feeder is correct. I mean it may require an EGC. All of the three criterion in 250.32(B) must be met before using it. If any of these three exist (basically anything conductive) you need an EGC included with the feeder.

Remember current will travel ALL paths from/to its source according to each level of resistance, not only the path of least. If bonding is done incorrectly it will cause current to travel where it does not belong. In 2008 bonding the neutral past the service disconnect and such is clearly an exception and only applies to existing premises wiring systems.
 
I'm suspecting that we didn't have a EGC in the vault so it wasn't present at the existing "premise" wiring. Still figuring out a code reference for bonding the neutral to the tap can with no EGC present.
 
wawireguy said:
I'm suspecting that we didn't have a EGC in the vault so it wasn't present at the existing "premise" wiring. Still figuring out a code reference for bonding the neutral to the tap can with no EGC present.
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250.24(A)(5), 250.142 and 250.32(B) say not. Once past the service disconnect you need EGC as listed in 250.118 and no bonding. The only exceptions are a separately derived system or the one exception to 250.32(B). Your faced with upgrading the feeders to quad or qualifying these multiple structures with 250.32(B).
 
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Let me add some more info. The overhead feeder or service? is coming from a vault with 13.2K volts feeding a 120/240 transformer. From that transformer in the vault we are hitting a disconnect. We are bringing a ground to the disconnect from the transformer. From the disconnect we are going over head to our temp service/feeder? with triplex. No EGC.

Now I'm starting to wonder where the service starts. At the disco in the vault or at the temp. There is no POCO as this is on a college campus.
 
wawireguy said:
Let me add some more info. The overhead feeder or service? is coming from a vault with 13.2K volts feeding a 120/240 transformer. From that transformer in the vault we are hitting a disconnect. We are bringing a ground to the disconnect from the transformer. From the disconnect we are going over head to our temp service/feeder? with triplex. No EGC.

Now I'm starting to wonder where the service starts. At the disco in the vault or at the temp. There is no POCO as this is on a college campus.
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The utility company usually determines the point of service. Who owns the 13.2KV XFMR?

Sounds like the secondary is single phase 3W delta (A, B, & N) and this may be determined service. It may also be determined the first disconnect past the XFMR as the service disconnect, the utility company probably didn?t furnish and install this. If so the distribution coming out of it are ?feeders?.

This still may not be a problem if installed in compliance pre ?88?, ?85? allowed the same exception as ?88? but also pre-existing installations.

If bonding is incorrect every time 110V circuitry is used current will travel every common path from/to its source, this usually creates problems in our electronic world but more importantly it can be dangerous touch voltage.
 
This is a head scratcher for me. I trust in whoever designed our install but want to understand it. College owns the 120/240 transformer in the vault. We installed a disconnect in the vault that is fed by the transformer, our aerial is fed from the load side. Then we go aerial to a temp(no meter). The aerial is a 3 wire triplex, two hots and a neutral. I'm curious if this is a new service we are establishing at the temp or if our service starts at the disconnect in the vault? And since it's a older existing setup even if our service starts at the disconnect are we required to take a ground to the temp? The disconnect is just for safety, in case there is a problem with the temp aerial.
 
Your service most likely is at the point where the campus 13.2 kV distribution connects to the utility supply. Everything on the load side of that is feeders and separately derived systems.
 
It is important to have an electrical engineer involved who is familiar with this type of distribution. The danger with these is they will work but may not be right.
 
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