Is running a neutral "through" a 3P disconnect switch legal?

[Enlightened]

I'm a facilities engineer. I have the following scenario: 480V / 208Y/120V transformer feeds a fused 3P disconnect, which then feeds an MLO panelboard. My electrican wants to run the neutral "through" the disconnect to the panelboard since we don't have a 4P disconnect. I looked extensively through the posts and in the NEC, and I haven't found anything that implies this is illegal. Can this be done as my electrician is proposing?

 

[qcroanoke]

I'm a facilities engineer. I have the following scenario: 480V / 208Y/120V transformer feeds a fused 3P disconnect, which then feeds an MLO panelboard. My electrican wants to run the neutral "through" the disconnect to the panelboard since we don't have a 4P disconnect. I looked extensively through the posts and in the NEC, and I haven't found anything that implies this is illegal. Can this be done as my electrician is proposing?

You don't really need a 4 pole disconnect unless you want to switch the neutral too. You probably should have a neutral bar in the disconnect for bonding purposes unless you did all of that in the xfmr.
Pulling the neutral through the disconnect is probably ok as long as all bonding and grounding was done in the xfmr. But I would look to see if a neutral bar is available for the disconnect and install it.

 

[Enlightened]

You don't really need a 4 pole disconnect unless you want to switch the neutral too. You probably should have a neutral bar in the disconnect for bonding purposes unless you did all of that in the xfmr.
Pulling the neutral through the disconnect is probably ok as long as all bonding and grounding was done in the xfmr. But I would look to see if a neutral bar is available for the disconnect and install it.

Thanks for the reply. I think I want to avoid pulling the neutral through. I've not seen that done before, and I didn't seem kosher to me.

 

[infinity]

The NEC would allow this unless this were a service disconnect.

 

[jap]

It's Your plant and you'r the Engineer. Have him land the Neutral on a Neutral Bar in the disconnect. If for no other reason than I might be doing work in there some day and I'm not a big fan of taking voltage readings to Ground when I'd prefer taking readings to the Neutral when its available.

JAP>

 

[fmtjfw]

The Neutral should follow along the ungrounded conductors and should be contained in the same raceways to reduce impedance and inductive heating problems.

Are you objecting to having the Neutral in the disconnect? How is the Neutral supposed to get from the source to the destination, by some other route? If the raceways are steel then the 4 current carrying conductors should be contained in the single, same raceway.

 

[fmtjfw]

See 300.3(B)

 

[infinity]

His electrician wants to run the neutral unbroken from the transformer through the disconnect and on to the panel. The ungrounded conductors will terminate to the line and load terminals of the disco.

 

[Smart $]

His electrician wants to run the neutral unbroken from the transformer through the disconnect and on to the panel. The ungrounded conductors will terminate to the line and load terminals of the disco.

Compliant.

 

[roger]

Compliant.

I second that.

Roger

 

[texie]

Compliant.

Compliant? Yes. Standard practice? No. Just kind of odd and not what you would expect to see.

 

[jap]

I agree with Post #2. You dont switch the Neutral in an install like this, but it is common practice to terminate the neutral on the neutral block in the disconnect, not pull it straight through unterminated.

It doesnt seem to me that the OP wants to switch the neutral in the disconnect, he's just not used to seeing the neutral not terminated in the disconnect. He indicated the disconnect was a 3 pole which evidently does not have a Neutral Block installed in it. The electrician probably opted to pull the neutral straight through since the neutral block wasnt there.

I may be wrong but I think the OP probably meant to say the disconnect does not have a "neutral block" instead of saying it doesnt have a "4th pole".

but I may be all wet on this one.

JAP.

 

[fmtjfw]

Thanks for the reply. I think I want to avoid pulling the neutral through. I've not seen that done before, and I didn't seem kosher to me.

His electrician wants to run the neutral unbroken from the transformer through the disconnect and on to the panel. The ungrounded conductors will terminate to the line and load terminals of the disco.

The red text led me to believe the OP wanted not to run the Neutral through the disconnect.

English is ambiguous: is the opposite of 'run the neutral "through"' 'terminate the neutral' or is it 'run it via another path'?

 

[iwire]

I'm a facilities engineer. I have the following scenario: 480V / 208Y/120V transformer feeds a fused 3P disconnect, which then feeds an MLO panelboard. My electrican wants to run the neutral "through" the disconnect to the panelboard since we don't have a 4P disconnect. I looked extensively through the posts and in the NEC, and I haven't found anything that implies this is illegal. Can this be done as my electrician is proposing?

How would you propose he run the neutral from the transformer to the MLO panel?

The NEC requires the neutral to be run with the ungrounded conductors.

 

[iwire]

Compliant? Yes. Standard practice? No. Just kind of odd and not what you would expect to see.

You have not been on my jobs.

Why would I purchase a neutral kit for the disconnect when I don't need one? We do our bonding in the transformer.

 

[fmtjfw]

230.75 Disconnection of Grounded Conductor requires a point at which you can break the neutral in a service.

I can find no equivalent requirement for a separately derived circuit.

The closest I can come is 250.142(A)(3) and 250.142(B) which discuss using the neutral for grounding.

 

[iwire]

The red text led me to believe the OP wanted not to run the Neutral through the disconnect.

Same here.

 

[qcroanoke]

The red text led me to believe the OP wanted not to run the Neutral through the disconnect.

English is ambiguous: is the opposite of 'run the neutral "through"' 'terminate the neutral' or is it 'run it via another path'?

I guess it's all in the interpretation. I did not read it that way.
Sorta like the NEC.

 

[kwired]

I guess it's all in the interpretation. I did not read it that way.
Sorta like the NEC.

Reading the title and first post I thought he was talking about running the neutral through a switch and possibly even a fuse, but later Q & A cleared up what the thread is all about IMO - which was is it ok to run the neutral unspliced through the disconnect enclosure?

My answer -for services no, for all other applications yes.

 

[jap]

I guess it's all in the interpretation. I did not read it that way.
Sorta like the NEC.

Same here, and good bad or indifferent if theres a neutral coming into a panel or a disconnect, I land it.