Single phase disconnect and fused neutrals

N

Nate1234

Member
Location
Indiana, USA
Occupation
Automation Engineer
I'm in an industrial setting. To comply with OHSA/NEC/NFPA, we like to have a lockable disconnect on any piece of equipment. Historically, most everything is 3-phase, and we'd just install a 3-phase, fused, lockable disconnect next to the machine.
We've got a single phase 120VAC boiler going in, and I expected the install would be similar, but I'm running into some questions:
- I know that according to NEC 240.22 we aren't supposed to fuse the neutral. Exceptions for 240.22 are when the overcurrent device opens all conductors in the circuit (which would not be true of a fuse), and in cases where it is required for motor overcurrent protection (this would be power to a control circuit and also a motor, the motor having it's own overcurrent protection, so I don't believe this applies).
- I understand that the disconnect device required for LOTO does not have to be fused, it's just typically this way on 3-phase for convenience.

I've checked a couple electrical suppliers, but I'm having a lot of trouble finding a single phase lockable disconnect. There are plenty of 2 pole disconnects where both poles are fused (would these be allowed?). I've seen others use what appears to be a light switch on the hot leg (compared to a typical three phase disconnect with a big pull handle, those seem suspicious to me).

What is the best practice when installing a disconnect device on a single phase circuit?
 
Nate1234 said:
...
I've checked a couple electrical suppliers, but I'm having a lot of trouble finding a single phase lockable disconnect. There are plenty of 2 pole disconnects where both poles are fused (would these be allowed?). ...
Click to expand...

I find both these sentences hard to believe, unless you meant a single pole disco. Any electrical supplier ought to have both fused and unfused 2-pole lockable discos in regular stock. In any case, there is nothing wrong with using only one pole of either a 2-pole or 3-pole disco, as Tom said.
 
Welcome to the forum.

You may switch the grounded conductor as long as you simultaneously open the lines, but not fuse it.
 
Nate1234 said:
I'm in an industrial setting. To comply with OHSA/NEC/NFPA, we like to have a lockable disconnect on any piece of equipment. Historically, most everything is 3-phase, and we'd just install a 3-phase, fused, lockable disconnect next to the machine.
We've got a single phase 120VAC boiler going in, and I expected the install would be similar, but I'm running into some questions:
- I know that according to NEC 240.22 we aren't supposed to fuse the neutral. Exceptions for 240.22 are when the overcurrent device opens all conductors in the circuit (which would not be true of a fuse), and in cases where it is required for motor overcurrent protection (this would be power to a control circuit and also a motor, the motor having it's own overcurrent protection, so I don't believe this applies).
- I understand that the disconnect device required for LOTO does not have to be fused, it's just typically this way on 3-phase for convenience.

I've checked a couple electrical suppliers, but I'm having a lot of trouble finding a single phase lockable disconnect. There are plenty of 2 pole disconnects where both poles are fused (would these be allowed?). I've seen others use what appears to be a light switch on the hot leg (compared to a typical three phase disconnect with a big pull handle, those seem suspicious to me).

What is the best practice when installing a disconnect device on a single phase circuit?
Click to expand...
You could use a dummy fuse, or simply splice the neutral in the disconnect enclosure, connecting the ungrounded conductor to the disconnect.
 
jaggedben said:
I find both these sentences hard to believe, unless you meant a single pole disco. Any electrical supplier ought to have both fused and unfused 2-pole lockable discos in regular stock. In any case, there is nothing wrong with using only one pole of either a 2-pole or 3-pole disco, as Tom said.
Click to expand...
Not in heavy duty. for sure. 3 pole only.
 
Nate1234 said:
I'm in an industrial setting. To comply with OHSA/NEC/NFPA, we like to have a lockable disconnect on any piece of equipment. Historically, most everything is 3-phase, and we'd just install a 3-phase, fused, lockable disconnect next to the machine.
We've got a single phase 120VAC boiler going in, and I expected the install would be similar, but I'm running into some questions:
- I know that according to NEC 240.22 we aren't supposed to fuse the neutral. Exceptions for 240.22 are when the overcurrent device opens all conductors in the circuit (which would not be true of a fuse), and in cases where it is required for motor overcurrent protection (this would be power to a control circuit and also a motor, the motor having it's own overcurrent protection, so I don't believe this applies).
- I understand that the disconnect device required for LOTO does not have to be fused, it's just typically this way on 3-phase for convenience.

I've checked a couple electrical suppliers, but I'm having a lot of trouble finding a single phase lockable disconnect. There are plenty of 2 pole disconnects where both poles are fused (would these be allowed?). I've seen others use what appears to be a light switch on the hot leg (compared to a typical three phase disconnect with a big pull handle, those seem suspicious to me).

What is the best practice when installing a disconnect device on a single phase circuit?
Click to expand...
I have done Universities and hospitals with high end, but reasonable Electrical Engineers. Every time I use a heavy duty single pole switch Hubbell 1221 for 20 amp, with a Garvin part number TOGLOK. Never once had a complaint. Hope this helps. I use these for most small circ pumps, VAV,s etc. Huge advantage never had an inspector want 36 inches of working space.
 
Strathead said:
I have done Universities and hospitals with high end, but reasonable Electrical Engineers. Every time I use a heavy duty single pole switch Hubbell 1221 for 20 amp, with a Garvin part number TOGLOK. Never once had a complaint. Hope this helps. I use these for most small circ pumps, VAV,s etc. Huge advantage never had an inspector want 36 inches of working space.
Click to expand...
That's where I was going.
 
Isn't that an unusual but almost universally acceptable situation...the fused or non-fused disconnect almost always is judged to fall under 110.26 but the 1221 is not :)
 
augie47 said:
Isn't that an unusual but almost universally acceptable situation...the fused or non-fused disconnect almost always is judged to fall under 110.26 but the 1221 is not :)
Click to expand...
I never thought about that when I did it but that's another good reason to use it.
 
augie47 said:
Isn't that an unusual but almost universally acceptable situation...the fused or non-fused disconnect almost always is judged to fall under 110.26 but the 1221 is not
Click to expand...
New to the 2023 NEC, 440.14 specifies that the disconnect for Article 440 equipment always has to meet the 110.26(A) working space requirements. So that would apply the 1221 heavy duty switch as well. But not relevant for the OP.

Cheers, Wayne
 
Order a switch with a solid neutral, problem solved, if does not have to be a heavy duty switch, a non fusible pullout A/C disco works too.
 
augie47 said:
Isn't that an unusual but almost universally acceptable situation...the fused or non-fused disconnect almost always is judged to fall under 110.26 but the 1221 is not :)
Click to expand...
I disagree with a non fused disconnect falling under 110.26 anyway, but I am just an electrician. I question even a fused one. Since an ohmmeter is all one needs to never need to work on one while energized.
 
Strathead said:
I disagree with a non fused disconnect falling under 110.26 anyway, but I am just an electrician. I question even a fused one. Since an ohmmeter is all one needs to never need to work on one while energized.
Click to expand...
That's a commonly debated subject. The 2023 Code clarified it in regard to HVAC disconnects in 440.14 by mandating 110,.26 applied to the disconnecting means.
 
Strathead said:
I have done Universities and hospitals with high end, but reasonable Electrical Engineers. Every time I use a heavy duty single pole switch Hubbell 1221 for 20 amp, with a Garvin part number TOGLOK. Never once had a complaint. Hope this helps. I use these for most small circ pumps, VAV,s etc. Huge advantage never had an inspector want 36 inches of working space.
Click to expand...
This is what I was referring to by "I've seen others use what appears to be a light switch on the hot leg".
In my experience, locking out a switch (in my case it would typically be something like an 800T-H2 selector with an 800T-NX446 lockable guard on it), is not generally used as an approved disconnecting means. This might simply be because such a switch would typically only lock out the control power. It just never sat quite right with me to use a switch as a disconnect, so I wasn't sure it that was acceptable in this case.

roger said:
What is the ampacity of the circuit?
Click to expand...
The boiler calls for 18.25 amps, so I was going to fuse it at 25amps.

Looks like my options are:
- a switch on the hot leg with a lockout device (if my circuit was below the amperage rating of the switch).
- use only one leg of a fused multiple-pole disconnect.
- use an unfused disconnect (I have since found some at another supplier, so they are more common than I initially found).

I've decided to go with a Siemens GNF221RA. I have the appropriate amount of clearance area as defined by 110.26 (even if it's not required, it's nice to have).

Thank you all!
 
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