Daisy Chaining Electrical Subpanels

[eeee]

Our maintenance group emphatically has said they do not want electrical subpanels daisy chained, but rather would like to have them have their own individual feeds from the MDP.

The problem with this is that this requires more breakers in the MDP and requires much more precious space on the wall in order to put in a MDP with two sections.

Is it considered a terrible design (from a maintenance perspective) to daisy chain a couple of subpanels?

I estimate that a repair would only take a couple of hours so that the diasy chained subpanels would only be off line for a couple of hours.

I know the NEC permits it.

 

[bphgravity]

Re: Daisy Chaining Electrical Subpanels

There's many more AHJ other than the elctrical inspectors and officials. What the boss wants, the boss gets.

From a personal standpoint, I don't see a real issue with that practice. As long as everything is labeled to indicate where the other overcurrent devices are disconnecting means are, noone should have a problem performing maintainance or repairs in a safe and effective manner.

 

[charlie b]

Re: Daisy Chaining Electrical Subpanels

It's not the repair time that is important (though I think you are being way overly optimistic), but rather the cost. For some facilities, the loss of power to even a portion of the system could shut down operations and cost far too much. So these types of decisions need to be based on two factors: The probability that something may have to be taken off line (for routine maintenance or for repairs) and the cost of the down time. It may prove cheaper, in the long run, to spend the extra money up front, and to expend the limited wall space, to put in the second MDP section. Or it may prove cheaper to just live with the occasional shutdown periods, and not spend the extra costs up front.

 

[kevinware]

Re: Daisy Chaining Electrical Subpanels

I guess I have to ask the question how critical will the equipment be that is powered by these daisy chained panels? I only ask that because we had a bad situation happen in our data center. We had one sub-panle with a 100 amp back-fed three pole breaker feed another sub-panel, and from that panel another 100 amp three pole back-fed breaker feed another sub-panel On a walk-through of the data center one day I reached up and grabbed the 2" EMT that fed the panels and the thing was real warm. I traced it back to the first 100 amp back-fed breaker and I couldn't even leave my hand on it, it was so hot. Well to make a long story short the breaker tripped and took down two full panels and some critical equipment. So I ask again, how critical is the equipment??

[ September 30, 2005, 08:16 AM: Message edited by: kevinware ]

 

[petersonra]

Re: Daisy Chaining Electrical Subpanels

I really prefer some means of shutting any individual piece of equipment off (in this case a PB) w/o having to shut off someting else I don't want off.

The maint guys have the right idea, although what you are advocating is Ok, it is soemthign that will eventually come back to bite you.

 

[eeee]

Re: Daisy Chaining Electrical Subpanels

The group consensus between the designer and us is that some unkown existing loads from the MDP will be moved to another subpanel so that each subpanel will have a feed from the MDP and no subpanels will be daisy chained to each other. I can always find wall space for a subpanel, even inside the building and not in the mech room if required. I had no wall space for adding another section to the MDP as originally wanted, since another section added to the MDP would be required to be placed adjacent to the original MDP using a short piece of conduit and power cable.

It will be the job of the construction contractor to determine the unknown existing loads, or if they are even existing. If the loads were not existing, we could have gotten away with not adding the subpanel in the design, eliminating contract modifications during the construction phase.