Two single 1P branch circuits with dedicated neutrals serving a single mechanical equipment, considered as a multiwire branch circuit?

[donghan82]

I was reviewing my colleagues' electrical design on a project and came across a mechanical equipment that required two 1P branch circuits serving a single equipment. I then wrote to provide a 2P circuit breaker or a two 1P circuit breakers with a handle tie to serve the equipment. However, the design intent of the two circuits was one branch circuit of the mechanical equipment will always operate and the second branch circuit will serve as a standby operation.

The code reference I referenced regarding this scope of work was NFPA 70 (NEC) Article 210.4 "Multiwire Branch Circuits". Is this particular situation considered as a "multiwire branch circuit" if each single pole branch circuit is served with a dedicated neutral? If yes, how can we accomplish this installation in a way to allow the second branch circuit to remain on if the first circuit breaker trips? If not, then would it be acceptable as shown with two 1P circuit breakers with no handle tie?

Thank you.

 

[roger]

No, it is not a Multiwire Branch Circuit, the article 100 definition is where you need to look.

Branch Circuit, Multiwire. A branch circuit that consists
of two or more ungrounded conductors that have a voltage
between them, and a grounded conductor that has equal
voltage between it and each ungrounded conductor of the
circuit and that is connected to the neutral or grounded
conductor of the system.

There is no NEC requirement to tie the two circuits together as you describe it however there may be some safety rational.

Roger

 

[donghan82]

Thank you for your response @roger . My colleague and I performed a code interpretation on Article 210.4 with other referenced code sections, including Article 100 "Definitions" as you noted in your reply. However, there was nothing that was clear enough to help support my case. Our preliminary resolution is (as this particular application does not apply to Article 210.4) to have the electrical contractor provide an signage to turn off both 1P branch breakers to ensure the equipment is fully de-energized prior to servicing the equipment.

 

[augie47]

Depending on the exact nature of your equipment, 422.30 mightb well apply as to signage, etc.

 

[infinity]

2-wire branch circuits are not a MWBC.

 

[tom baker]

The persons servicing the equipment should be qualified and know how to test for voltage.

 

[tthh]

Thank you for your response @roger . My colleague and I performed a code interpretation on Article 210.4 with other referenced code sections, including Article 100 "Definitions" as you noted in your reply. However, there was nothing that was clear enough to help support my case. Our preliminary resolution is (as this particular application does not apply to Article 210.4) to have the electrical contractor provide an signage to turn off both 1P branch breakers to ensure the equipment is fully de-energized prior to servicing the equipment.

I know some manufacturers make independent trip handle ties - at least Square D does. This could accomplish your safety goal. The way it works is one breaker can trip and it doesn't trip the adjacent breaker. But, the handle tie doesn't allow you can't turn only one off.

 

[jap]

This is not a MWBC issue, it is a disconnecting means issue.

With 1 circuit always needing to be kept energized while the 2nd also needing to be kept energized as a backup, will require the disconnecting means to be kept separate.

Using a handle tie on 2 separate single pole breakers to accomplish this is unrealistic to anyone who's ever tried it.

Best bet would be to install the disconnecting means at the point of use, and, as you suggested, some type of labeling that the equipment is being fed from multiple power sources.

JAP>