SRT 10 KVA Input Circuit Breaker size

[BillP]

Hi team ,

Could you please explain h below issue we facing with SRT model 10 KVA UPS.

1. We purchased the new 10 KVA UPS from APC, The model name is SRT10KXLI. As per the Installation manual, it mentioned regarding the External input circuit breaker - 80 Amp (16 Sq.mm) is required.

2. But we have the older model SURT type 10 KVA UPS, which is required 63A external input circuit breaker. 

So please explain technically why the SRT model need an 80 A breaker ? 

[BillP]

Hello - 

The SRT10K has a Unity Power Factor design which gives it a higher wattage capacity despite having the same VA capacity.

• SRT10KXLI - 10.0 KWatts
• SURT10000XLI - 8.0 KWatts

In order to accommodate the higher wattage, these units require additional breaker capacity. The current SRT8KXLI is an 8.0 KWatt unit like your older SURT10000XLI model. 

Thanks

Liam

[TellItLikeItIs_apc · Accepted solution]

Rule of thumb - 5A per kW ie 50A for a 10kW UPS plus 10% for charging. That equals 55A. the next breaker size up is 63A

Unless you are running your UPS at 100% load, which is as rare as hens teeth, and bad practice anyway, the 63A breaker will suffice.

The manufacture has to cover for worst case and then over engineer on top.

For cable size, this will depend on distance between the supply, the UPS, and the load. In most cases 16mm cross section cable will be over sized. Over sized cable isn't a bad thing, except for your pocket. Get someone to carry out a cable calc. An electrician will need to sign off the completed installation anyway so they are best placed to advise.