Multiple (3) sources of power in the same panel

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NRGross

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Hi All,

I just received a request from a customer that wants 3 sources feeding into one power distribution panel that would then be providing power to equipment inside the room where the panel is located. I am assuming he wants this because he would rather feed power into one place and distribute it throughout the room rather than having separate power drops from outside of the room for each piece of equipment (all sources are located within the same building). I can see this being very tricky using separate disconnects for each source and trying to interlock the disconnects with the door. So, my question is other than labeling that there are more than one power source feeding this enclosure are there any other code requirements for something like this? I had a veteran panel builder say to me to just avoid the headache and option for 3 separate panels rather than one, but from what I can find there are no code violations as long as I am using a separate disconnect for each source and is well labeled stating that this enclosure has more than one source. Please correct me if I'm wrong and please share any tips/experience if you have done something like this in the past.


As an example the power requirements to be in one of the panels are as follows:

480VAC 3p 60A
240VAC 3p 30A
120VAC 1p 30A


Thanks!

-Nathan
 
NRGross said:
Hi All,

I just received a request from a customer that wants 3 sources feeding into one power distribution panel that would then be providing power to equipment inside the room where the panel is located. I am assuming he wants this because he would rather feed power into one place and distribute it throughout the room rather than having separate power drops from outside of the room for each piece of equipment (all sources are located within the same building). I can see this being very tricky using separate disconnects for each source and trying to interlock the disconnects with the door. So, my question is other than labeling that there are more than one power source feeding this enclosure are there any other code requirements for something like this? I had a veteran panel builder say to me to just avoid the headache and option for 3 separate panels rather than one, but from what I can find there are no code violations as long as I am using a separate disconnect for each source and is well labeled stating that this enclosure has more than one source. Please correct me if I'm wrong and please share any tips/experience if you have done something like this in the past.


As an example the power requirements to be in one of the panels are as follows:

480VAC 3p 60A
240VAC 3p 30A
120VAC 1p 30A


Thanks!

-Nathan
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I don't see how you could do this; a set of busbars can only be at one voltage. You could have 480/277V in the panel and a transformer to generate the 240V three phase with a center tap (high leg) to make the 240/120V, but I don't see how to get it all in a single panel.
 
What do you mean by panel?
Do you want three Independent panel boards in a single/common enclosure? I have seen these 'power centers' from all of the major manufacturers, including custom shops. They are fairly common in big box stores and other places where they don't want to look at conduits.
 
jim dungar said:
What do you mean by panel?
Do you want three Independent panel boards in a single/common enclosure? I have seen these 'power centers' from all of the major manufacturers, including custom shops. They are fairly common in big box stores and other places where they don't want to look at conduits.
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By panel I mean a single or multiple back panels mounted directly inside an enclosure. Mounted to these back panels would be disconnects, circuit breakers, distribution blocks, terminals, etc... hopefully I'm describing this clearly...
 
I think what he is talking about is actually closer to a UL508a industrial control panel someone would fabricate rather than a regular panelboard.

I don't see anything really wrong with the idea provided he is careful to label where the disconnecting means are for each source.

Personally, I think I would just mount 3 MCB panelboards with the appropriate voltages adjacent to each other.

An extra box is going to take up a lot of room.
 
petersonra said:
I think what he is talking about is actually closer to a UL508a industrial control panel someone would fabricate rather than a regular panelboard.

I don't see anything really wrong with the idea provided he is careful to label where the disconnecting means are for each source.

Personally, I think I would just mount 3 MCB panelboards with the appropriate voltages adjacent to each other.

An extra box is going to take up a lot of room.
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Yes, this is exactly what I am talking about I just didn't know how to word it properly. The only problem I see is with safety and wanted to get other thoughts on how to interlock the door properly so someone cant walk up to the door and open a half energized enclosure.

The reason I am not really looking into a breaker panel is because the equipment being powered already have their own protection and he is wanting an enclosure in each of the rooms he is building that will distribute power to equipment and is expandable.

Say if another conveyor is to be added in the future we would be taking power from the enclosure local to the room rather than running conduit from a breaker located on the other side of the building.
 
It’s a bad plan IMHO. It will be a nightmare to deal with the arc flash potential from one live source being present in the panel when you turn one off to work on it. So that means you will have to don the bunny suit or lose ALL 3 sources just to open the box. Seems cumbersome.

Assuming that killing everything is OK, then you can get a 6 pole disconnect switch for the 240 and 480, then add an aux contact for the 120V. Finding an aux contact rated for 30A, but I seem to recall they are available. Now whether you can get that for a 6 pole disconnect, that may be a challenge. Worst case, a smaller door mounted disconnect for the 120V.
 
It is also a bad idea because of the tap rules. You cannot just tap off a bus bar with any old conductor size.

He would be so much better served with separate panel boards. They will have the busing and tap protection built in with plenty of room for expansion if planned properly.

He is probably a cheapskate thinking he can save money this way.
 
Jraef said:
It’s a bad plan IMHO. It will be a nightmare to deal with the arc flash potential from one live source being present in the panel when you turn one off to work on it. So that means you will have to don the bunny suit or lose ALL 3 sources just to open the box. Seems cumbersome.

Assuming that killing everything is OK, then you can get a 6 pole disconnect switch for the 240 and 480, then add an aux contact for the 120V. Finding an aux contact rated for 30A, but I seem to recall they are available. Now whether you can get that for a 6 pole disconnect, that may be a challenge. Worst case, a smaller door mounted disconnect for the 120V.
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These are also very good points Jraef. I agree with this and is why I like the 3 enclosures idea much better than the all in one. Customer is really pushing for all in one so I'm attempting to present all scenarios to him. Through door Interlocks are nice and all but most of them can be bypassed. I was also thinking 6 pole for the 3ph supplies(seems hard to find) and a door mounted disconnect with electronic door interlock for 120. I am under the assumption that he is okay with killing all power to the box but in my head this is downtime that no one will want to deal with after it happens a few times and will eventually be bypassed by the maintenance crew.


I was also thinking two door enclosures with a barrier in the middle to isolate my 3ph panels from each other with the door mounted 120 disconnect one on of the sides. This would lead to just one side having to be shut off depending on what needs to be worked on. But at this point the enclosure will cost a fortune....I think the 3 separate boxes win again...

PS peter if you're reading this I think you're on to something about the last thing you said...!
 
NRGross said:
PS peter if you're reading this I think you're on to something about the last thing you said...!
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I run into these kind of guys now and then. They look at the price of an empty box and think they are going to save a ton of money. I gave up a long time ago trying to educate them, because they are usually not able to be educated because of their fixation on 2% of the total job cost.
 
Jraef said:
It’s a bad plan IMHO. It will be a nightmare to deal with the arc flash potential from one live source being present in the panel when you turn one off to work on it. So that means you will have to don the bunny suit or lose ALL 3 sources just to open the box. Seems cumbersome.

Assuming that killing everything is OK, then you can get a 6 pole disconnect switch for the 240 and 480, then add an aux contact for the 120V. Finding an aux contact rated for 30A, but I seem to recall they are available. Now whether you can get that for a 6 pole disconnect, that may be a challenge. Worst case, a smaller door mounted disconnect for the 120V.
Click to expand...
Bringing this back up after doing more digging and looking into parts. I have found many 6 pole disconnects and many of them having HP ratings. Since these disconnects for example: ABB part number OT63F6 have HP ratings for 240/480, how would I interpret and abide by the rating when feeding multiple conveyors/ pieces of equipment. Again, these breakers are only feeding other panels/disconnects that already have properly sized overcurrent protection for branches and none of the motors are sized greater than the HP ratings on any of the new disconnects. Hopefully this question made sense... not really sure how else to word this...
 
NRGross said:
Bringing this back up after doing more digging and looking into parts. I have found many 6 pole disconnects and many of them having HP ratings. Since these disconnects for example: ABB part number OT63F6 have HP ratings for 240/480, how would I interpret and abide by the rating when feeding multiple conveyors/ pieces of equipment. Again, these breakers are only feeding other panels/disconnects that already have properly sized overcurrent protection for branches and none of the motors are sized greater than the HP ratings on any of the new disconnects. Hopefully this question made sense... not really sure how else to word this...
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I am without my NEC today (left my PC at the office and my work phone at a job site yesterday, it was a bad day…), but there is a rule on sizing disconnects for multiple loads, I believe it is 115% of the total FLCs of each load. Maybe someone else can look it up and cite it.
 
Jraef said:
I am without my NEC today (left my PC at the office and my work phone at a job site yesterday, it was a bad day…), but there is a rule on sizing disconnects for multiple loads, I believe it is 115% of the total FLCs of each load. Maybe someone else can look it up and cite it.
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Woof rough day... sounds like someone had a base case of the Mondays...;)

Yes, so that mostly answers my question and I thought of a better way to word it. Since the disconnect will not be serving as branch circuit protection directly to any of these motors, I need not worry about HP rating of the disconnect and only typical load calculations as you stated?
 
NRGross said:
Woof rough day... sounds like someone had a base case of the Mondays...;)

Yes, so that mostly answers my question and I thought of a better way to word it. Since the disconnect will not be serving as branch circuit protection directly to any of these motors, I need not worry about HP rating of the disconnect and only typical load calculations as you stated?
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Correct.
 
Jraef said:
Correct.
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And sizing of a 6 pole disconnect will be sized based off of the higher of the two loads? If I have 60A 480V and 50A 240V I would size for 480 and a trip would occur if one of the circuits were to draw more than 60A? Just weird to think about the two circuits in one breaker, but I guess since the loads are not on the same circuit they would not add. Am I thinking about this correctly?
 
705.12.(B)(2)

(3) Busbars. One of the methods that follows shall be used to determine the ratings of busbars in panelboards.
(a)The sum of 125 percent of the power source(s) output circuit current and the rating of the overcurrent device protecting the busbar shall not exceed the ampacity of the busbar.​
Informational Note: This general rule assumes no limitation in the number of the loads or sources applied to busbars or their locations.​
 
topgone said:
705.12.(B)(2)

(3) Busbars. One of the methods that follows shall be used to determine the ratings of busbars in panelboards.
(a)The sum of 125 percent of the power source(s) output circuit current and the rating of the overcurrent device protecting the busbar shall not exceed the ampacity of the busbar.​
Informational Note: This general rule assumes no limitation in the number of the loads or sources applied to busbars or their locations.​
Click to expand...
Thank you for adding this note. With this I made sure to double check my distribution blocks ampacity rating.
 
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