Blowing transformers

    I have 2 units in a school hallway, running seperate rooms, that are blowing transformers. I have already replaced one transformer, only to have it blow again within a half hour. The units are on seperate circuits, not connected in any way. Does anyone have any idea what could cause this?
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On Fri, 3 Dec 2010 02:51:52 +0000 (UTC), snipped-for-privacy@sdf.lonestar.org wrote:

    Transformers have needs, too, you know .....
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Too much current draw, and no overload protection for the transformer.
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loss.
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to spend on this in the morning, and was hoping there was a common problem that I couln't see. The units are only 3 or 4 years old, worked fine all summer, and I assume worked in heating for a month or so.
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On 12/2/2010 8:51 PM, snipped-for-privacy@sdf.lonestar.org wrote:

In the morning, if I can walk, I have to go to a customer's store to repair network cable that mice chewed up. For some reason, the little critters love to chew on plastic insulation. Did you install new transformers with same current rating? Somewhere on the transformer there will be a label or printing indicating the VA rating. 40VA is a popular size but in a school or institution the low voltage may run electrically operated dampers and /or valves. You would need a transformer with a higher current rating.
TDD
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a 50VA. I have a lot of spare 75VA, would there be any danger in trying one?
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Before or after you find what the additional current draw is???
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On 12/2/2010 9:51 PM, snipped-for-privacy@sdf.lonestar.org wrote:

Do you have a DMM with a 10amp shunt for measuring current? A larger transformer might burn up the low voltage wiring. I would suggest taking the 75VA transformer and putting a 5amp fuse in line with the low voltage so you can check the current draw. The 75VA unit may have a built in circuit breaker from the factory. Of course check the voltage going into the transformer because some goofy electrician may have hooked that line to a higher voltage. Sometimes it's the simplest thing that's causing a problem.
TDD
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The 75VA does have its own breaker. I'll try that in the morning just to get them some heat. Any ideas what I should be looking for as to what could cause this? It would be a pretty huge coincidence, the way they quit. Thanks.
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On 12/2/2010 10:41 PM, snipped-for-privacy@sdf.lonestar.org wrote:

A critter could have chewed up some wires or the input voltage is too high. If you have three phase power with a high leg, someone might have moved the circuit breaker that supplies power to the transformers to a high leg. I assume the transformers were hooked to a 120VAC supply or in the case of a business or institutions, the transformers may require 208-240VAC supply connected to the proper pair of wires on a multi-voltage input control transformer. Always check the basics and don't assume you have the correct power going to something. The multimeter is your friend. The first thing I would do is to check all voltages without the air handler controls being hooked up, if those readings are proper, start checking current draw for the control system. A lot of control transformers have separate 208 and 240VAC connections. If your supply is 240VAC and you connect the 208VAC winding, you can possibly let all the magic smoke escape from the transformer because you will get a lot higher secondary voltage than 24VAC. :-)
TDD
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I have one question for you? You said that you replace transformer have try or bother checking amperage in and out Then perhaps you question maybe some what legit??? Even so it does not make sense for me asking these but what the heck!!

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snipped-for-privacy@sdf.lonestar.org wrote:

Turned out to be the contactors in a heat bank inside the room. Thanks for your help.
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Yes, got one room up and going. Turns out there was a lightning strike in the spring. Guess that would explain the seperate rooms going down.
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