Sources with different voltages for UL508A Panel

[PabloQG]

We have an ICP with 6 motor starters at 208V and 3 motor starters at 480V. Because of tiny electrical room space, we need to reduce the quantity of panels. We are a UL508A shop.

I know that UL508A allows for multiple sources to be connected to a single panel, in which case it states several rules to be followed for markings, overcurrent protection and so, but all of those assume the same voltage for all sources.

So, questions:

• Is it acceptable to have multiple sources at different voltages?
• If so, should the panel be rated and marked with a slash voltage or only with the lowest voltage level?
• For SCCR calculations, should use smaller or greater voltage rating?

PD: We are a UL508A panel shop. I already sent this question to our UL representative, but they takes ages to answer.

 

[Jraef]

No rules against it, but it’s not a good idea in most cases. You will need to have a way to kill power to BOTH sources before opening the door, which is a pain. Your label would have to list both voltages and you would need to calculate and list the SCCR for each source separately. But from an NFPA70E standpoint, this would be problematic in terms of working on one system without disconnecting the other, so every time something goes down on one system, everything needs to be shut down to work on it.

But it is possible.

 

[paulengr]

We have an ICP with 6 motor starters at 208V and 3 motor starters at 480V. Because of tiny electrical room space, we need to reduce the quantity of panels. We are a UL508A shop.

I know that UL508A allows for multiple sources to be connected to a single panel, in which case it states several rules to be followed for markings, overcurrent protection and so, but all of those assume the same voltage for all sources.

So, questions:

• Is it acceptable to have multiple sources at different voltages?
• If so, should the panel be rated and marked with a slash voltage or only with the lowest voltage level?
• For SCCR calculations, should use smaller or greater voltage rating?

PD: We are a UL508A panel shop. I already sent this question to our UL representative, but they takes ages to answer.

1. Slash voltages are when neutrals are used like 208/120.
2. Each source gets a label. I like to hang the control power transformer outside the box for heat reasons.
3. Why does it even matter? Isn’t it simpler to just make a box for each and have a control signal terminal strip for inter-box connections?