new tanning salon

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finster1

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We have a TANNING store that has a calculated load of 400A . The utility promised to bring in 240v 3phase. When the dust settled they brought in 3ph 208v 400a to disconnect. I have been asked to size a transformer capable of going from 208v3 ph to 240v 3ph 400a. Can anyone help me with the calculation of where I would begin. These stores normally use buck boosters on each of the tanning beds but the owner would like to put a single transformer and feed the panel instead.
 
If you want full load of 400 amps, then the tranwsformer = 400a x 1.73 x 0.24 = 166 kva. Pick a size.
 
Before you jump onto the single transformer route, note that most 3 phase 240/120 transformers have a stringent reduction in the neutral capacity so you would need to watch you 120 volt loading.
Whether you decide to use a buck and boost or single transformer, I would suggest supplying a panel for the tanning beds only and leaving the other loads on the 208/120 panel.
(That would also reduce the size transformer needed as you would only be supplying the beds)
 
Unless I'm very tired this morning, you could install a bazillion kVA transformer and you're not going to create a 240V 3Φ 400A service on the secondary if you're truly limited to 208V 400A on the primary side.

Bob accurately sized a full winding isolating transformer size that could be used but you should note that the maximum secondary current would be 347A on the secondary with 400A on the 208V primary side.

I thought you were asking for a boost configuration/size that could be used. I calculated ~ 11kVA per Φ or 34kVA 3Φ but you should check my numbers and you would want some safety factor so maybe use something in the 45kVA range. Keep in mind you still only have 347A capability on the secondary side. You also now have the problem where do you wire your 120 receptacles etc. to?

I don't know how much load you're talking about for the beds, but maybe a potential solution is one boost autotransformer supplying a smaller "bed panel" with 240V and the rest of the facility supplied from your given 208Y/120 supply? This would eliminate the boost at every bed which the owner seems to desire?

Oops, looks like Augie and I were thinking similar and he typed faster....
 
finster1 said:
We have a TANNING store that has a calculated load of 400A . The utility promised to bring in 240v 3phase. When the dust settled they brought in 3ph 208v 400a to disconnect. I have been asked to size a transformer capable of going from 208v3 ph to 240v 3ph 400a. Can anyone help me with the calculation of where I would begin. These stores normally use buck boosters on each of the tanning beds but the owner would like to put a single transformer and feed the panel instead.
Click to expand...

Here is how I would price it up.

Standard 400 amp 208Y/120 service, use this panel(s) to directly supply every load in the space except the tanning beds.

Install a second 3 phase panel to supply just the tanning beds, supply this panel from the 208 panel using two buck / boost transformers sized for the projected load. This panel will have no neutral and strange voltage readings from line to ground but will be close to 240 line to line.

The two small buck/boost should cost about 25% of a single large standard transformer.
 
cord and plug tranformer

cord and plug tranformer

I have made for lady. A portable buck/boost transformer with two cords 208 in and 240 out. Plug it in and tuck it under the machine. When she moves it from location to location the cord caps match-up. I worked my self out of several easy service call on that brain storm,
 
finster1 said:
We have a TANNING store that has a calculated load of 400A . The utility promised to bring in 240v 3phase. When the dust settled they brought in 3ph 208v 400a to disconnect. I have been asked to size a transformer capable of going from 208v3 ph to 240v 3ph 400a. Can anyone help me with the calculation of where I would begin. These stores normally use buck boosters on each of the tanning beds but the owner would like to put a single transformer and feed the panel instead.
Click to expand...
Just for fun you might want to double check voltage requirements of beds, the situation I keep running into is tanning beds that need 208 volts but all that's available in dwellings here is 240. I noticed you said stores normally use buck boosters--so is voltage normally 208?
 
iwire said:
Here is how I would price it up.

Standard 400 amp 208Y/120 service, use this panel(s) to directly supply every load in the space except the tanning beds.

Install a second 3 phase panel to supply just the tanning beds, supply this panel from the 208 panel using two buck / boost transformers sized for the projected load. This panel will have no neutral and strange voltage readings from line to ground but will be close to 240 line to line.

The two small buck/boost should cost about 25% of a single large standard transformer.
Click to expand...

If the Op decides to go this route, I would highly suggest using a trough under the buck/boost transformers. There is little to no room in these for your connections. I don't know why they haven't made these with more room in them for connections, especially for 3 ph. I had to literally take a floor jack and put it under the bottom cover to press the wires in to get the cover back on.:rant:
 
400 A @ 240 v 3 phase = 166.3 KVA

400 A @ 208 V 3 phase = 144.1 KVA

If 400 A @ 240 is needed, where is the extra approximately 22 KVA going to come from?
 
kwired said:
That is about 1/8 of the capacity of the desired service, you don't feel it needs possible consideration?
Click to expand...


I think that there is very little chance the original load calc was more than 348 amps at 240.

I highly doubt that the calculated load was 400 amps and I sure you really don't think it came out to a nice round figure like that either.
 
iwire said:
I think that there is very little chance the original load calc was more than 348 amps at 240.

I highly doubt that the calculated load was 400 amps and I sure you really don't think it came out to a nice round figure like that either.
Click to expand...

I kind of figured he didn't have a total load calc that came out to exactly 400. But also figured it was very likely anywhere between 201 and 399 to justify wanting 400 amps to begin with.


225 amp service cost about the same as 200, 250 thru 400 all cost about same.
 
kwired said:
400 A @ 240 v 3 phase = 166.3 KVA

400 A @ 208 V 3 phase = 144.1 KVA

If 400 A @ 240 is needed, where is the extra approximately 22 KVA going to come from?
Click to expand...

Thats not it works. If you need 166 kva at 240 volts the the amps = 400 amps
You will need to supply 166 kva at 208 volts. 166/(,208 x 1,73) = 461 amps.
 
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