MWBC DCing means: 210.4(B) vs. 240.15(B)(1)

Status
Not open for further replies.
Electron_Sam78

Electron_Sam78

Senior Member
Location
Palm Bay, FL
It looks to me like 240.15(B)(1), which says that L-N loaded MWBCs can have single pole breakers for each hot leg with or without handle ties, is invalidated by 210.4(B) which says MWBCs must have all hots legs disconnected simultaneously at point of origin and then 210.4(C) which says all MWBCs must be L-N loads (with some exceptions). Is that correct? What's the deal? Is it a conflict?

[2008 NEC paraphrased]
 
infinity

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Sounds like they need to remove the bold words:

240.15 Ungrounded Conductors.
(A) Overcurrent Device Required. A fuse or an overcurrent trip unit of a circuit breaker shall be connected in series with each ungrounded conductor. A combination of a current transformer and overcurrent relay shall be considered equivalent to an overcurrent trip unit.
FPN: For motor circuits, see Parts III, IV, V, and XI of Article 430.
(B) Circuit Breaker as Overcurrent Device. Circuit breakers shall open all ungrounded conductors of the circuit both manually and automatically unless otherwise permitted in 240.15(B)(1), (B)(2), and (B)(3).
(1) Multiwire Branch Circuit. Except where limited by 210.4(B), individual single-pole circuit breakers, with or without identified handle ties, shall be permitted as the protection for each ungrounded conductor of multiwire branch circuits that serve only single-phase line-to-neutral loads.
Click to expand...
 
charlie b

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
roger said:
Actually, IMO 210.4(B) as it is worded now is useless and even more dangerous than it was in earlier code cycles.
Click to expand...
You lost me on that one, Roger. Can you say why it is more dangerous now? :confused:

But back to the question, keep in mind that 240 is about overcurrent protection. The article in question is telling us that single pole breakers can be allowed to serve as overcurrent protection for a MWBC. That is all that 240 is going to care about. I agree that the bold words "or without" should be removed. But they don't have to be, since it does say, "Except where limited by 210.4(B)." That sends us to the requirement for handle ties for single pole breakers, so we don't get to go around that requirement.
 
jumper

jumper

Senior Member
Location
3 Hr 2 Min from Winged Horses
charlie b said:
You lost me on that one, Roger. Can you say why it is more dangerous now? :confused:
Click to expand...

I am not speaking for Roger, but I may have an idea of why he said this.

There is a large amount of people who believe that the handle tie requirement will lead to a lot of people doing more live work.

The reason is that it will be more of a hassle to convince customers to let electricians shut off power on three breakers, when he only needs to work on one light/device etc. So the electrician maybe more likely to work it hot.
 
renosteinke

renosteinke

Senior Member
Location
NE Arkansas
I believe that the 210.4 rule applies only to residences; that commercial locations need not have the breakers linked to each other.

Bear in mind the rarity of 3-phase power in residences.
 
Status
Not open for further replies.
Top