Disconnects for small dry-type transformers

[a10jp]

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?

 

[waross]

Kitchen equipment rated for 220V, 230V, and 240V is commonly operated on 208V supplies.
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

 

[rbulsara]

I am not aware of NEC requirement for "local" disconnect on the primary side of LV transformers. There is one for HV transfoermer in tunnels etc.

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.

 

[waross]

I stand corrected on the issue of disconnect switches. I apologize for the erroneous information.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[advidana]

Disconnecting means and overcurrents protection for transformers fall under the tap rules in the NEC 2008 check there ( Article 240.21). There is a lot of rules so read them all. You may find what you need to deal with your electrical contractor.

 

[jraef]

I don't see a violation in that photo, but I do see a very bad idea... They are placing multiple open core-and-coil transformers on a rack in a louvered multi-door enclosure. First big storm with wind blown rain might make for some interesting fireworks in that panel. I would also expect to see some major corrosion of core laminations and connection points in short order. Outdoor transformers are typically "potted" in an epoxy-sand mixture to protect the windings and laminations, then the terminations are in a junction box designed to prevent moisture from coming into contact with them. The transformers they are using in that photo appear to be those typically used inside of indoor equipment such as Switchboards, Control Panels and Motor Control Centers which are usually NOT going to be in areas where moisture ingress is likely.


"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

 

[a10jp]

Bill, please do not apologize. My description could be confusing.

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.

 

[alehman]

This looks like a rather questionable setup to me. Even with local disconnects, realistically it seems unlikely that all of the transformers will be shut down to do maintenance. Is this arrangement listed by a recognized testing lab per the local authority's requirements?

Have the transformer manufacturers been consulted as to adequacy of cooling?

 

[a10jp]

Yes, alehman, you are correct. At first glances, you wouldn't service any of these units unless a group of the them have been de-energized. But based on the numerous thoughts and discussions, we need to change these transformers to an enclosed type, which we have already been in discussion with the installers.

 

[jraef]

One of the arguments for that will be the issue of "Arc Flash" protection. Even at low voltages, the fact that nobody can enter that enclosure without killing ALL sources of power is, at best, problematic. I don't see how any inspector familiar with the latest code changes is going to allow that. Is this project being inspected?


"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

 

[a10jp]

Hi jraef, because of the issues mentioned above. We have already asked complete replacement of these units to sealed enclosed dry-type units. I am assuming the arc-flash problem you mentioned is related to the open coil issue. We are partially inspecting all these issues as it goes, and safety concerns for accessing these units without completely de-energizing groups of the units was one of many concerns I have sent in to be addressed.

 

[a10jp]

I have reviewed NEC Art 240.21 on locations of overcurrent protection for branch circuits. In this case because the circuits goes from the electrical panels inside to outside, I am wondering if Art 240.21(B)(5) for outside Taps of unlimited length, and where it says on (3) The overcurrent device for the conductors is an integral part of a disconnect means or shall be located immediately adjacent thereto; and where it says on (4) the disconnect means is installed at a readily accessible location...

 

[waross]

A couple of things to check before ordering the new 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

 

[a10jp]

Hi Bill, I have checked before, but these kitchen equipment is ordered based upon the voltage selection the cusotmer has picked. Needless to say, they put have not put a lot of thoughts or checks into it, that's why we wind up with different voltage equipemnt everywhere. But I will make sure to check again. And thanks for the tips on the transformers.

 

[waross]

Heating equipment will take a little longer to come up to temperature initially but will generally have no problem holding a set temperature on a lower voltage.
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

 

[REDDOG]

Try Article 110.3B this whole thing ia a code violation.

 

[a10jp]

Hi Bill, many thanks for your offer. I will defintely ask everyone again. It will take some time to document all the kitchen equipment at this time.

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.

 

[alehman]

Reddog,
Not necessarily. It depends on how the transformers are listed and labeled.