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Isolation transformer - getting full, rated kva

I am having my electrician install a Topaz 5kva isolation transformer (TP-91905-68) that will power 4 dedicated circuits in a seperate, dedicated sub panel. The electrician has 220v coming in off the main panel into the Topaz and then 120v going out of the Topaz to the sub panel. I thought I had read in one of the posts here that in this type of installation, if not done correctly, you cold actually only be getting 1/2 of the rated output of the isolation transformer (so, 2.5kva versus 5kva).

If anyone has knowledge of this particilar isolation transformer in this type of configuration and can shed some light on the situation (if in fac there is an issue) I would be very grateful.
dangelod
dangelod OP
40 posts
 
No, no owners manual and was not able to find one online.
ngjockey
1,042 posts
 
It's 220/440-120/240. That means that it will have 4 output conductors (not including ground) and they would be wired in parallel for 120V and series for 240V. It's possible to use only half but it's hard to imagine an electrician doing that.

Don't remember if Topaz uses the H1-H4/X1-X4 convention. If it's new, there should be some sort of schematic inside the "end" enclosures.
saygrr
72 posts
 
I asked the electrician here at work. The wattage does not change when voltage is halved or doubled. the amps would halve or double. I think it would be a good idea to get an owners manual and make sure it is wired correctly. My owner manual does not include your model. If it did I would have made a copy and mailed it to you. Ngjockey is right there might be a schematic in side the cover. What you are doing is a very good idea but make sure it is wired correctly.

Enjoy the music
jea48
4,486 posts
 
It's 220/440-120/240.
01-04-12: Ngjockey
Ngjockey,

If that is indeed the case, and each primary winding is wound for 220V and the secondary will output 120/240V then I would first bench test the xfmr. Good chance the voltage at his service electrical panel is 240V to 246V. What will be the output of the xfmr? Above 124V ain't good.....

Saygrr,

The electrician is right.
But just to add there are two 120V secondary windings.
Each winding is good for 2.5 KVA each.

Say the electrician was not instructed by Dangelod how he wanted the secondary output of the xfmr configured and the electrician installed the xfmr and new panel and wired the xfmr and panel for 120/240V.

Dangelod may have told the electrician he wanted all 4 branch circuits wired from the same leg of the panel and not from both.

In that case the loads connected to just one leg to neutral would be only connected to one 2500Va winding of the transformer.

So to get the full rating of the transformer both secondary windings must be connected in parallel (120V out), same for both primary windings must be conned in parallel, (if as Ngjockey has indicated dual windings 220/440V), to get the full 5 KVA rating.
ngjockey
1,042 posts
 
Assumed this was for Europe or somewhere international.

Might be some confusion with derating for balanced AC, which isn't the question here and not trying to confuse the OP.
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