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mdshunk said:
Yup, but it's bad design for this sort of duty, in my opinion, considering the recent code changes related to MWBC's
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As much as I like MWBCs I have to agree with Marc, bad place to use them.
 
But, since FL hasn't adopted the 2008 yet, I would use them for every circuit I could.

Roger
 
Now, would anyone of you like to share your views? I brought this up about two months ago, and it was shot down without explanation. I am not one to argue.
 
76nemo said:
Now, would anyone of you like to share your views? I brought this up about two months ago, and it was shot down without explanation. I am not one to argue.
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In a nutshell, nobody likes you much.

:)D )
 
First off always remember I hate everyone. :D


Second......

76nemo said:
Now, would anyone of you like to share your views? I brought this up about two months ago, and it was shot down without explanation. I am not one to argue.
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What views are you asking about?

I will be glad to ramble on about MWBCs, it certainly will not be the first time. :D
 
76nemo said:
Electronics, harmonics, and overheating issues. Remember now???
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Electronics and their associated additive harmonics are of little concern.

How many overheated MWBC neutrals truly attributed to the above items have you repaired?

Roger
 
roger said:
Electronics and their associated additive harmonics are of little concern.

How many overheated MWBC neutrals truly attributed to the above items have you repaired?

Roger
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This is where I did not want to go. To answer your question Rog, none,....zippo. My point was the same as Bob's and Marc's, this is where I would not choose to use them. I am not going to get into a p*ssing match with anyone, again, I am not one to argue. My point is this is definetly not a scenario where I would choose the short cut. Wouldn't the facility mentioned be the last place we would want PQ issues??????
 
roger said:
Electronics and their associated additive harmonics are of little concern.

How many overheated MWBC neutrals truly attributed to the above items have you repaired?

Roger
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You wouldnt be saying that 15 yrs ago when they were starting fires. When the 4 wire of a lighting circuit was too hot to touch.
 
76nemo said:
This is where I did not want to go. To answer your question Rog, none,....zippo.
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As I thought.

quogueelectric said:
You wouldnt be saying that 15 yrs ago when they were starting fires. When the 4 wire of a lighting circuit was too hot to touch.
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In over 30 years of wiring hospitals, 90% of the circuits I have run have been MWBC's with no heating problems even with magnetic ballasts involved. :rolleyes:

The pictures below are in a NICU and almost every conduit has a MWBC in it. This is only one electrical closet of probably 100 or more in this facility all of which are loaded with MWBC's.

NORMsystems.JPG


CR-EQsystems.JPG



The problem with your hot circuits was most likely to do with loose connections or overloaded conduits.

Roger
 
quogueelectric said:
You wouldnt be saying that 15 yrs ago when they were starting fires. When the 4 wire of a lighting circuit was too hot to touch.
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Have you anything more then a rumor?

I have been running MWBCs for lighting as long as I have been in the trade, never an issue.

These circuits? where they derated when run in conduits with other circuits?

Where they maxed out in general?

Where they continuous loads?
 
76nemo said:
My point was the same as Bob's and Marc's, this is where I would not choose to use them.
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Like Marc, my only reason for not using them in a Hospital situation is strictly the fact the NEC now required a common disconnecting means and that will be a maintenance issue.

I have no worry what so ever that a EKG machine is going to place so much harmonics on the branch as to be a danger.

Besides ..... even if you run all two wire branch circuits the harmonic issue still pops up on the panel feeder and the transformer supplying it.
 
Personally, I try to spec life safety equipment (I would consider quite a lot of hospital equipment life safety) or large draw items (like X-Rays, dental chairs, portable suction) on a separate circuit, or do one or two rooms as one circuit. Which ever the panel will allow.
 
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