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Running 240V then bringing back down to 120V with transformer?

Running 240V then bringing back down to 120V with transformer?

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  #1  
Old 11-14-15, 02:05 PM
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Running 240V then bringing back down to 120V with transformer?

Hi.
My church has a very old building and restroom is a small building outside.
When this restroom was built, they only pulled 14 AWG wire and it is powering everything in the restroom.
There is no heat in the bathroom, so there is issue with frozen toilet during winter time. To keep the place warm, we used 2 small space heater (1 for girl's room, and 1 for men's room.) This ends up overloading the circuit and tripping the breaker.

The best solution would be to run another circuit from breaker panel to restroom, but that requires digging under gravel and small patch of asphalt. I would like to avoid this if possible.

So, what I was thinking is converting existing 120V 15A circuit to 240V 15A circuit and install 240V baseboard heaters.
Then use 240V to 120V transformer to power existing 120V circuits in restroom. (lights, fans, heat tapes for pipes, and outlets)

I know this will work electrically, but not sure if it is safe. Using 240V to 120V transformer will have no neutral and both prongs of outlet would become hot.
Bonding one wire from secondary to ground will create neutral, but not sure if that really can be considered neutral.

Do you think this is ok?
Will it be code compliant?

Any better suggestion?


Thank you.
 
  #2  
Old 11-14-15, 03:57 PM
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What else is being powered in the bathroom? This could work in theory, but I don't think is will be cost effective. Also, you would still be limited to the size of heaters that could be installed. 2 heaters at 1000 watts each (plug in space heaters are normally 1500 watts) would run about 8.3 amps on their own at 240 volts. There will also be losses from the transformer. I doubt this option will work very well.

The other issue is the location of a sub panel and transformer. That equipment cannot be installed in a bathroom. You can install them outside if the proper equipment is used. (3R)

Could you go overhead with the feeder? Another option is to install gas heat and run it off a propane tank.
 
  #3  
Old 11-14-15, 06:02 PM
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I'm not allowed to add second circuit? I didn't know that.
This restroom basically is like detached garage. Don't they sometimes have multiple circuit running to garage?

I can carry more load (in terms of watts) with same current at higher voltage. No?

Restroom is very small. Just enough to have a toilet and a sink per girl's room and men's room.

I thought about overhead drop, but doesn't that require thicker cable? (6 AWG is smallest I saw.)
 
  #4  
Old 11-14-15, 06:05 PM
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Don't they sometimes have multiple circuit running to garage?
No. That is a code violation if it is a detached garage. If they need multiple circuits they run a feed to a subpanel in the garage and then run the circuits from that. That would also be your best solution.
I can carry more load (in terms of watts) with same current at higher voltage. No?
No. Watts = volts x amps. If you double the voltage with a transformer you cut the amps in half. At 240 volts you would have 7.5 amps available before subtracting transformer losses.
I thought about overhead drop, but doesn't that require thicker cable?
Actually if that was THWN you saw it is probably not suitable because it isn't intended to be used outside conduit and isn't sunlight resistant. What would work would be sunlight resistant 10-3 UF cable supported by a 1/8" wire cable. You would then install a four space 60 amp breaker box at the rest rooms. You could use that to provide two 120v/15a circuits for the heaters and one 120v/15a circuit for lights. It would be fed by a 240 volt 30 amp breaker in the main panel.

You might squeak by using 12-3 UF on a 20 amp multiwire circuit without needing a subpanel (especially if you ran the heaters on low only). A multiwire circuit would give you two 20 amp 120 volt circuits with out needing a subpanel. Use one circuit per rest room to provide light and heater in each rest room. The multi wire circuit would require two handle tied single pole breakers or one two pole breaker but would count as only a single feed.
 

Last edited by ray2047; 11-14-15 at 06:28 PM.
  #5  
Old 11-14-15, 06:08 PM
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2 60 W Light bulb, 1 fan, 2 heat tapes, 2 heated garden hose.
These are all the load. Not much load at all until heater is plugged.

I was thinking about 3 ft baseboard heater. Which are 700 W at 240V (about 3A).
So, total of 6A load.
There is a small storage room behind restroom, which can be used to store transformer.
Is sub panel required?
 
  #6  
Old 11-14-15, 06:14 PM
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No. That is a code violation if it is a detached garage.
Looks like best way would be to run new wire and install a sub-panel.
What would be the cheapest way to run overhead line?
I don't think I can just run UF-B wire..

If you double the voltage with a transformer you cut the amps in half.
I think you misunderstood what I was saying. I was going to run 240V from main panel to restroom and install 240V heaters. This way I can install higher wattage heaters.
Transformer will only power devices that require 120V. Lights, fans, and heat tapes. Which I think would be 3 A at most.
 
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Old 11-14-15, 06:33 PM
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I think you misunderstood what I was saying. I was going to run 240V from main panel to restroom and install 240V heaters.
I did misunderstand. You wouldn't need a transformer in that case. Use 240 volt LED bulbs and heat tape.
Looks like best way would be to run new wire and install a sub-panel.
See my edits to the post above.

Apologies for misreading your post. I have deleted my first reply.
 
  #8  
Old 11-14-15, 06:47 PM
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Use 240 volt LED bulbs and heat tape.
I wish I could, but 1 of the heat tape is not accessible because whoever built bathroom put floor on top of plumbing. Also no crawl space. Restroom is built on top of the septic tank. (Very weird setup).
There also is a issue with fan and heated garden hose, which are 120V.

What would work would be sunlight resistant 10-3 UF cable supported by a 1/8" wire cable.
How should I attach UF cable to 1/8" messenger wire? Using zip ties will be enough? (UV resistant zip ties of course.)

Thanks.
 
  #9  
Old 11-14-15, 08:15 PM
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Using zip ties will be enough? (UV resistant zip ties of course.)
From what the pros here have written the zip ties just don't last. I'd suggest spiral wrap the messenger wire around the UF cable. Same way an overhead drop to your house is spiral wrapped around the messenger. I'd suggest plastic coated steel cable for the messenger wire. The messenger wire will need to be grounded to the system ground.

If you go for a subpanel you will need to add a ground bar to it and be sure the neutral bar is isolated. A Ĺ"x8' ground rod will be needed at the subpanel also.
 
  #10  
Old 11-15-15, 06:58 AM
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You can deliver 3600 watts intermittent or 2900 watts continuous (minus transformer losses) via the original two 14 gauge conductors using 240 volts. A transformer with center tapped secondary in the outbuilding will provide 120 volts.

This is still probably not enough for your needs.

Be aware of any restrictions on heat tape, which may vary from brand to brand.

With a new feed, the old wires can be used for a switch at the main building to control a light at the outbuilding. The light should be powered from the outbuilding.
 
  #11  
Old 11-15-15, 08:41 AM
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2 60 W Light bulb, 1 fan, 2 heat tapes, 2 heated garden hose.
These are all the load. Not much load at all until heater is plugged.
I was thinking about 3 ft baseboard heater. Which are 700 W at 240V (about 3A).
So, total of 6A load.
Is 700 watt heaters going to be enough? Not sure how cold it gets in VA.

IMO this could work but you would need to add up everything that is running on 120 volts. The fan, the heat tapes, and the heated garden hoses. Anything that heats normally can use a fair amount of power which could push you over capacity. Adding everything up will then allow you to figure out what size transformer you would need. A simple 240 to 120 volt transformer would be enough to carry the 120 volt equipment rather then a full transformer with a center taped neutral. You would still need a sub panel (240 volt only) for the heaters and to feed the transformer.

All that above said, I do still think running a new feed (underground or overhead) is a better option. However, if you could get by with a transformer it could work.
 
  #12  
Old 11-15-15, 10:33 AM
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I'm thinking cost and complexity make a transformer less desirable than a subpanel and overhead line.
 
  #13  
Old 11-15-15, 11:16 AM
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A 240v to 120v 1 KVA transformer would run about $250.. Either way he would need a sub panel so that would be a wash. Depending on how long of an overhead run it is, plus mast(s) and misc. parts (poles, knobs, etc) it also might be the same, or more, as a transformer.

Installing a transformer would not be that complex. He would just need to change the breaker to a two pole, then in the separate building install a small sub panel (240 volt only). Off the sub panel he would have the branch circuit(s) for the heaters, and one feeder to the transformer. Off the secondary of the transformer he would connect the branch circuit to the 120 equipment.
 
  #14  
Old 11-16-15, 08:19 AM
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With the cost and complexity of the transformer installation, and the cost of masts + lashing on the overhead option, I see the best option as going underground with UF-B cable (I'm assuming you have volunteers to dig the trench for free). Use 10-3 or 8-3 UF-b cable to a 4 space subpanel in the outbuilding; from a 30A or 40A double pole breaker in the main panel. My gut feeling is that this is the cheapest option on materials that will give you enough power to the the heat and lights safely.

Make sure all of your outlets in this restroom are GFCI protected, even the ones driving the heat tapes! This is a serious safety concern in an outdoor bathroom.
 
  #15  
Old 11-16-15, 01:35 PM
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A couple of the pros have mentioned risers if overhead but I wonder if they are needed. Maybe if the cable could be run gable to gable there would be enough height without risers and a simple drip loop used where it leaves the church and enters the rest room. If that is allowed what would minimum height be over a drive way?
 
  #16  
Old 11-16-15, 02:55 PM
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For an area with pedestrians only: 10'

Light traffic (a.k.a. personal vehicles only, no trucks or delivery entrances): 12'

Any type of public access road, parking lot or driveway: 18'

These are minimum clearance heights under the lowest point of the aerial cable for normal flat graded land. If the cable goes over any building or body of water the heights are be different. Note that to have enough slack for sag of the cable and enough to make an effective drip loop you usually need to add at least 2 feet to the minimum height on either side of the cable. That means if you need to clear 12' in the center, you'll want to mount it at least 14' on either end; or some other arrangement like 13' on one side and 16' on the other side.
 
 

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