Two single-pole breakers for a 240V loadcenter

[ronalvarez]

Hello,

I am new to the forum. I have a question regarding an electrical design I got my hands on. First, I am not located in the US, I live in Panama Central America, however we go by the NEC.

What I saw was the following:
One single phase, 2 poles, 120/240V loadcenter being fed by two single 120V UPS units, each one protected by a single pole breaker at the source. So, Basically, I have a 240V loadcenter being protected by two single pole breakers. I advised the designer to change the breakers and UPS units, however the client has the two 120V UPS available and wants to use them, and since the UPS units are 120V, the designer considers they should be protected by single pole breakers.

Is there any especific reference or NEC article I can use to either the breaker issue and UPS issue. I have been looking for documentation to back up my advise but have not been able to find it.

Thanks in advance.

 

[Joethemechanic]

How are you synchronizing the two 120 volt UPSs? That would be my main concern. You could end up with an overloaded neutral. And hot leg to leg voltage could be anything between zero and 240

 

[ronalvarez]

How are you synchronizing the two 120 volt UPSs? That would be my main concern. You could end up with an overloaded neutral. And hot leg to leg voltage could be anything between zero and 240

If I understand your question correctly, I could only assume there shouldn't be any alteration between an UPS input and output voltages (such as angle displacement), meaning that if I have 240V measurement between both UPSs inputs, I should have the same voltage between their outputs. Am I right? or this is not usually the case?.

Down below there is a screenshot of the riser. I forgot to mention in my previous post that there is a double throw switch between UPS units and loadcenter (TTA). Also, this is a 3-phase system, so it is really 208V, not 240V. Loadcenter TTA is still single phase (2 poles).

 

[ptonsparky]

I wouldn't trust that you get what you want. Better do some testing.

 

[jim dungar]

Simply connecting the grounded (neutral) point of the UPS's may not be sufficient unless the UPS's are designed for this connection, such as employing a sync connection/function.

The majority of 120/240v system have two, in sync, 120V sources connected in series, like two windings on a common transformer core or taking the midpoint of a single winding.

 

[Joethemechanic]

Simply connecting the grounded (neutral) point of the UPS's may not be sufficient unless the UPS's are designed for this connection, such as employing a sync connection/function.

The majority of 120/240v system have two, in sync, 120V sources connected in series, like two windings on a common transformer core or taking the midpoint of a single winding.

And even if they have a sync function, they might be designed for parallel sync

 

[ronalvarez]

I wouldn't trust that you get what you want. Better do some testing.

Agreed. I also believe the main issue with this configuration comes when there is a power outage and the battery starts working. I don`t think the UPS is designed to keep the same angle phase as the utility power, so no 208V at their outputs.

Besides the UPS issue, any recommendation on whether there should be a two pole breaker protecting the loadcenter, instead of two single poles.

Thanks in advance.

 

[jim dungar]

From a saftey perspective, as in disconnecting power from the panel, I believe all poles must be opened simultaneously and be capable of being locked.

 

[ptonsparky]

Curious.

How big are these units that you feel you need over current protection on the output side of them?