Disconnects for small dry-type transformers
Disconnects for small dry-type transformers
(OP)
I am looking for a code reference concerning dry-type transformers that are being installed inside an enclosure outside the bldg. The situation here is we have a list of kitchen equipment where the user has ordered for the wrong voltages, as such we have to provide small individual step-up dry transformers for them. The problem is all the equipments have different utilization voltages, 220, 230, 240, 315, 450, etc.., some are small like 2KVA, single phase, and soemas as large as 3-phase 15KVA. The service voltage is 120/208. However, because thereis no space inside the area where the equipments are, we have to put them outside the bldg, with an semi-weatherproof enclosure, but with ventilation.
The installation they are doing in my opinion was incorrect. One of the problems (among many) I saw was there are no disconnect switches ahead of the transformers in the enclosure for service maintenance. So what we have is the branch circuit breakers at the load panel, to the transformers outside, then to disconnects switches for equipment inside, and then the equipment.
A few folks has ssaid that based upon the size of the load, 2KVA ~ 15KVA, you may not need disconnects. I looked at the Code and did not find anything that says you need disconnects for transformers. However common sense says I need to have. Any idea which is right, and why?
The installation they are doing in my opinion was incorrect. One of the problems (among many) I saw was there are no disconnect switches ahead of the transformers in the enclosure for service maintenance. So what we have is the branch circuit breakers at the load panel, to the transformers outside, then to disconnects switches for equipment inside, and then the equipment.
A few folks has ssaid that based upon the size of the load, 2KVA ~ 15KVA, you may not need disconnects. I looked at the Code and did not find anything that says you need disconnects for transformers. However common sense says I need to have. Any idea which is right, and why?






RE: Disconnects for small dry-type transformers
While there may be some equipment that needs the correct voltage, electric stoves, hot water tanks, and clothes driers are typically rated for 230 volts and operated on 208 volts.
But, given the interesting voltages, have you also checked the frequency rating of the equipment?
There may be exceptions to the disconnect rule if the installation will be serviced by qualified persons.
I would be more concerned with OSHA compliance and arc flash hazards. Small equipment that is cord and plug connected may use the plug as the disconnect. Unfortunately permanently installed equipment is not allowed to be plug connected. This may be the basis of the suggestion that a disconnect is not needed.
I am on the road and don't have a code book to hand.
I would also suggest one large transformer feeding a 139/240V panel to feed as many of the loads as possible.
Has the local AHJ been contacted and seen the installation yet?
Please let us know how this turns out.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Disconnects for small dry-type transformers
What is required by Code is the "overcurrent" protection for the conductors on the secondary side, generally if they are longer than 10 feet before terminating in first overcurrent device.
RE: Disconnects for small dry-type transformers
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Disconnects for small dry-type transformers
RE: Disconnects for small dry-type transformers
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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RE: Disconnects for small dry-type transformers
jraef, what you said is my exact concern. Has these transformers been confirmed with mfr for use in outdoors; why do we sleect open coil (cast coil?) option when the insulation of the coil can most l-ikelt be contaminated and damaged by the weathering elements; what about surge protection since these units are now moved outdoors; how do we deal with maintenace on these units; and yes, secondary protection of the transformers per ART. 450.3. For one, we are asking the installers to replace with sealed units. I wish we can install them inside the bldg, bu there is juts no space in the kitchen or anywhere, that's why the installers resort to this.
But about the disconnect, I was just applying common sense first, then the code. With all the enegerized units lying next to each other, and without any disconnect means anywhere in sight, how can we call this safe, if someone were to access and service these outdoor transformers units and indoor circuit breakers are not secured...again, I think I am looking about secured procedure, accessible by qualified personnesl, readily accessible within certain distance, etc..I will take a look at Art 240.21 as advidana has suggested.
RE: Disconnects for small dry-type transformers
Have the transformer manufacturers been consulted as to adequacy of cooling?
RE: Disconnects for small dry-type transformers
RE: Disconnects for small dry-type transformers
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies
RE: Disconnects for small dry-type transformers
RE: Disconnects for small dry-type transformers
RE: Disconnects for small dry-type transformers
1> Auto transformers will be smaller, cheaper and possibly have less losses.
2> Has the kitchen equipment been evaluated to determine if voltage adjustment is required for each piece of equipment?
You may not need all of the transformers.
If most of the equipment is rated for 220V, 230V or 240V, then use one transformer to boost the voltage to 240V and feed a breaker panel. Use that breaker panel to feed the equipment. Again an auto transformer will be cheaper.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Disconnects for small dry-type transformers
RE: Disconnects for small dry-type transformers
A booster heater on a commercial dish washer will take a little longer and add a little time to the cycle time. This may be one of the first places that low voltage in the kitchen will be noticed. It depends on the throughput of the kitchen. In one application the slightly extended cycle time for a dish washer will be of no consequence. In another kitchen with a different work load an extended cycle time may be unacceptable. It's a local judgment call.
The point is, you may not need to adjust the voltage for every piece of equipment.
I suspect that there is a good chance that the installation will be started over. You will have a chance to correct some of the mistakes. If you wish to give us a list of the equipment and the voltage ratings I am sure we can give you some suggestions as to what must have the proper voltage, what may not need the exact voltage and what will run on the 208 volt supply.
A 240:24V boost rated transformer wil boost 208 volts up to 229 volts. That should handle anything rated from 220V to 240V.
A 0.5 KVA 240;24V transformer connected as an auto transformer will supply 20.8 amps at 229 volts. That's 4.763 KVA. That means that you can usually replace a 5 KVA transformer with a 0.5 KVA transformer. Saves a lot of money.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Disconnects for small dry-type transformers
RE: Disconnects for small dry-type transformers
REDDOG, do you mean code violation strictly from the standpoint the transformers are open coil, or the enclosure are not suited for the applications? Accordingly the manufacturer stated this is made for outdoor use. But there are other code violation that are not obvious in that picture.
RE: Disconnects for small dry-type transformers
Not necessarily. It depends on how the transformers are listed and labeled.