Really short MWBCs

Status
Not open for further replies.
ron said:
Is the OP clear in the details if this was a single phase or three phase installation?
Click to expand...

I left that out of my original post- there's a mix of single and three phase installations, but all were done with 2p breakers and the phases reasonable balanced. I'm not concerned about that.

realolman said:
I think if you wanted 2 wire circuits, you should have specified them. Although I can certainly see your point, there is no reason for the installers to have wanted them.
Click to expand...

That's really where I was trying to get, that there aren't any technical or engineering reasons that I was missing. I'll certainly be more careful about this in the future.

realolman said:
After all, if the vendors are blowin the breakers, it is their "fault", not the electricians' . Hey, it's a festival... lighten up. :smile:
Click to expand...

Definitely their fault, OTOH hell has no fury like a food vendor that can't make product. I try to avoid that, it upsets people :D . However, after a vendor trips out for the third time in a day, I've pretty much used up whatever hurrying power I'd reserved for them.

Thanks everyone.
 
ron said:
zbang,
Did they use 2 pole breakers for MWBC's on a three phase system?
Click to expand...

And why would this be a problem? If each MWBC is only two hots and a noodle, it doesn't matter. If all three phases enter the same gang box to service the recepts, then there is an issue.

As someone who has done a lot of shows and temp venue setups, I agree that the use of MWBC was a poor choice for the main reason mentioned, i.e. one vendor's trip would possibly take another vendor's power with it.

zbang:

Do you think it would be cost-effective for you to exchange all the DP breakers for singles, add the extra neutral wire, and keep the DP breakers to resell to defray the cost of fixing this mess? Perhaps start with the panel with the "worst offenders" and work you way around to the others?

That is what I would do, just to end the aggravation.
 
I would have used the MWBC with single pole circuit breakers.

It soulds like someone was assuming or expecting a job spec that was not brought up at the time of bid / quote.

The same could be said about the type of cover used. Such as why would they use plastic boubles when they allways break?

IMO 2 or 3 ploe CB for MWBC feeding lighting or rec is not the greatest idea but one pushed by the newer codes.

We are on a older code cycle.
 
realolman said:
I am assuming that the reason for the handle tie is to identify ( and de energize )all the phase conductors associated with the MWBC.

Couldn't there be some reasonable effective alternative ? Maybe something colored that would snap on the two breakers? Maybe some sort of tie that did not operate all the poles, but would identify them?
Click to expand...

IIRC, the "handle tie" is only to "de-Engergize" all conductors associated with the MWBC.

This is a safety issue, so there are no "surprise" hot conductors in the box.

I do not think there is any "alternative" to this.
 
Before the 2008 NEC MWBCs did not have to have handle ties unless they supplied a single device.

With the adoption of the 2008 NEC ALL MWBCs must have a means for simultaneous disconnection.
 
I think, considering the use of the outlets, its a poor design.
I wouldn't risk someone taking out someones elses booth by using two pole breakers.
Double poles cost more, I dont see the savings.
 
I would have done this with a MWBC if I wasn't under the '08 NEC.

It might be a case of the installer doing it the way he always has, then realizing that under the '08 NEC he needed a 2 pole breaker. Or possibly the inspector pointing out the need for 2 pole breakers.
 
I've been involved with several festivals and my experience has been that you have to keep everything as simple as possible. We label each circuit at each end and only have one ground fault protected receptacle per 120 v circuit. No MWBC. There are venders involved and when you leave the site anything and everything will be plugged into receptacles. It's mass confussion when a circuit blows at these events so at least have the vendor that has a problem with equipment deal with his problem and not effect somebody else. Use the "KISS " method , spend a few extra bucks on install and it will pay off in the long run. You company will get a lot of exposure at an event either good or bad . If problems are minimal usually good but look out if they have major problems that could have been averted at a little extra cost. Companys pay for good advertising but a bad install at an event could give you some bad advertising that may cost a lot more than the few extra bucks spent to keep it simple s____d.
 
SmithBuilt said:
It would be nice if one of the breakers tripped the other would stay on. Of course you would want the breakers that indicate they are tripped to help with trouble shooting.
Click to expand...
I think there's a company called FPE that makes a breaker or two that does just that!:D

It sounds like someone did what someone always does. I believe that's the ANSI 30 standard*.:roll:

Or, it's an application of WIT** principals.

*I've been doing that for 30 years!

**WIT= What's In Truck
 
Status
Not open for further replies.
Top