- Thread starter charlston
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Efficiency of tranny? If you have a 50kVA tranny don't you have 50KVA output available regardless of efficiency of the tranny, the difference being on the input power vs output power?For the calculated load for conductor sizing, OCPD, etc your continuous loads are at 125%.

Transformers are sized for actual connected load. Sizing the tranny depends on efficiency of tranny and future design.

I am referring to peak efficiency. Usually somewhere between 88% and 95% IIRC. It varies with models.Efficiency of tranny? If you have a 50kVA tranny don't you have 50KVA output available regardless of efficiency of the tranny, the difference being on the input power vs output power?

Ok, but unless you have a fairly steady load 24/7 that peak efficiency level might be somewhat meaningless I would think.I am referring to peak efficiency. Usually somewhere between 88% and 95% IIRC. It varies with models.

Not sure, but I thought that was the max output, not the max efficiency load.I thought that the manufacturer has figured all of that out and the KVA rating is the maximum rating of the transformer?

Many transformers are 95% so it is kinda moot.

What about in terms of the OP's question, if the calculation came to 50 kva would you need larger than a 50 kva transformer?Not sure, but I thought that was the max output, not the max efficiency load.

Many transformers are 95% so it is kinda moot.

I size the tranny to the actual connected load not the calculated load. I do not factor in for continuous loads.What about in terms of the OP's question, if the calculation came to 50 kva would you need larger than a 50 kva transformer?

IOW, if the lighting load is actually 5000VA, I use that number for tranny.

For branch circuit, feeders and service size, I factor in 125% for continuous loads.

On "delicate loads", I sometimes look at the voltage flicker a transformer gives when big motor loads are started.I size the tranny to the actual connected load not the calculated load. I do not factor in for continuous loads.

IOW, if the lighting load is actually 5000VA, I use that number for tranny.

For branch circuit, feeders and service size, I factor in 125% for continuous loads.

I usually shoot for the following:On "delicate loads", I sometimes look at the voltage flicker a transformer gives when big motor loads are started.

Constant load min 50%

Average load 75%

Peak load max 90%+

Basically a rule of thumb that I was taught, seems to work.