# Tapping 110v from 220



## shell70634 (Mar 24, 2022)

I'm planning the replacement of my air compressor.  I'm adding a homemade cooling system between the compressor and tank.  The fan requires 110 volt.  I have 220 volt at the site for the compressor motor.  I really don't want to run another 110 circuit and thought I might tap into one side of the 220.  Good idea?  Bad idea?  If it's unsafe or not advisable for other reasons I will search for a 220 fan motor for the cooling system.  The compressor is outside the building under cover with the switch inside the building.  Making everything run from one switch is preferred.


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## SLK001 (Mar 24, 2022)

It depends on the wiring for the 220V.  Some 220V wiring has 4 wires - two hot, a neutral and a ground.  With this config, you can easily tap off 110V.  If you only have three wires, two hot and a ground, you _*can *_get 110V from a hot and the ground, but I believe that this violates all electrical codes.  Your better option would be to simply get a 220V fan.


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## markba633csi (Mar 25, 2022)

You can use a hot and ground to get 110v- I won't tell anyone
For a light load like a fan it should be fine


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## Winegrower (Mar 25, 2022)

There are some pretty inexpensive down converters on eBay, depending on the power you need.   That could be effective.


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## epanzella (Mar 25, 2022)

My lathe is 220 but the lights over it are 110v. I just fed the lights with one leg of the 220 line. Lots of appliances do this right from the factory. An electric range uses 220 for the burners but one leg of 110 to power the clocks, timers, lighters, ect. If you have a large 110v load it would be best to split it up over both legs of the 220 line but just make sure that neither leg is driven over the capacity of the 220v breaker which is merely two 110v breakers slaved together so if one trips it takes the other one with it.


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## rabler (Mar 25, 2022)

For this reason, I run 4 wire for 220V circuits even if I only use a 3 prong receptacle, I leave the unused neutral wire capped in the box.


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## rwm (Mar 25, 2022)

Am I mistaken on this but are some ground wires smaller in gauge than the conductors in the same cable?


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## matthewsx (Mar 25, 2022)

rabler said:


> For this reason, I run 4 wire for 220V circuits even if I only use a 3 prong receptacle, I leave the unused neutral wire capped in the box.


This^^^^

If you do it with the ground you will forget, or not be around some day and someone can make a very bad mistake. 

I have my shop wired this way through an extension cord, if you don’t have neutral please use a transformer. Just because something works doesn’t make it right.  

John


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## woodchucker (Mar 25, 2022)

rwm said:


> Am I mistaken on this but are some ground wires smaller in gauge than the conductors in the same cable?


they are supposed to be the same size or bigger.


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## woodchucker (Mar 25, 2022)

matthewsx said:


> This^^^^
> 
> If you do it with the ground you will forget, or not be around some day and someone can make a very bad mistake.
> 
> ...


not if you split it off at the compressor. Then it's part of the compressor.


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## Bi11Hudson (Mar 25, 2022)

The whole idea is used regularly by many appliances, often using the ground lead as a neutral to get 120 volts. A proviso here is that the appliances are 'UL' approved so acceptable to insurers. If you have a neutral in the box, that whole point is moot. Now, to advisability of the idea. Yes, you can do it, *but*. . . And No, it is illegal (not to code) and insurers will do whatever they can to not pay. Just what you needed, an ambivalent answer, nei.

The issue I have (as a retired electrician) with what you spoke of is the use of one switch. The switch should be a (fusable?) disconnect, not a lighting switch. And further, the circuit should be sized so that the compressor AND the fan running does not exceed 80% of the breaker capacity. By rights, even a 240 volt motor on the fan should have a separate circuit feeding it. That covers the legal aspects of what you're doing. A disclaimer on my part, if you will. As far as will it work, it has been done countless times across the country and usually not found out.

A comment was made above about making it part of the compressor. The up side of that is that the code essentially ends at the plug. The cord is part of the appliance (compressor) and not subject to the code. Just make sure to connect at the cord, ahead of the pressure switch.

.


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## shell70634 (Mar 25, 2022)

Thanx for all the replies. You’ve given me the solution.


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## mksj (Mar 25, 2022)

You have not indicated if you have a neutral line at the compressor and/or plan to pull in a neutral. You cannot use a neutral form another circuit and if you do pull a neutral line for the compressor circuit the gauge needs to be sized for the circuit and not what it is running. You also have the issue that if you have the compressor on say a 30-50A circuit, all the wiring needs to sized rated for the breaker including wiring to the fan, the fan would need to be fused and/or have it own breaker/overload device. Alternative when a neutral is not available, what is commonly used is a step down transformer 240->120, they can be picked up for not much and the VA rating would be a minimum of fan V x Amps = VA plus some margin. Fans typically do not take much current. The transformer may have ratings for input/output current and require fusing/breaker. Even if you were to buy a 220V fan, which would seem to be the most cost effective solution, I would have local fusing breaker for it. I bring 4 wire power to my machines and breakout local circuits with MCCB breakers or fusing for the 120/240V subsystems. Wiring is rated for the overload device and thermal rating of the connections.

My compressor after-cooler is bolted to the belt cage and uses the air from the mechanical fan which then cools the compressor.


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## SLK001 (Mar 25, 2022)

All oven receptacles now are 4 wire for new installation.  IIRC, the only three wire receptacles left that meet NEC are for welders.


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## rabler (Mar 25, 2022)

woodchucker said:


> they are supposed to be the same size or bigger.


As you get into large wire size, the ground is allowed to be smaller.  For example 6/3 nm (romex) uses   iirc a 10 ga ground wire.


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## rabler (Mar 25, 2022)

Using the ground wire as a current carrying conductor is a very bad idea, _*regardless of whether done in the building wiring, or in the appliance*_.

The whole point of a ground is a redundant safety, in case something goes bad, like a poor wiring connection.  Say you are in a shop run on a sub-panel.  If the ground wire between the subpanel and main panel fails, and you have the compressor wired with the fan to ground, you have now connected the ground wire to 120V.  This means that EVERY GROUNDED DEVICE has it's frame at 120V when the compressor fan is "on".  Touching any of those frames could result in a shock, including grounded metal outlet boxes, etc.  Even things plugged in to the shop through a GFCI will have this issue.  Nor would such a shock trip the GFCI, or a breaker.  The current will be limited by the draw through the fan, but it doesn't take that much to kill someone if the current path goes through the wrong place in their body.  Your only physical evidence of the problem, other than the issue with shocks, will be that the compressor fan doesn't run.

Yes, that is a contrived worst-case scenario.  But if everything is operating correctly, a ground is totally unnecessary, which is why early wiring didn't use grounds.  In the above scenario, having a ground rod wired to the shop subpanel would mostly mitigate the issue.  (But the ground and neutral should not be bonded in that subpanel).


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## whitmore (Mar 25, 2022)

Old-school 120V accessory circuits,  like in my stove, had a 15A fuse, not simply wire connection, because
the stove breaker does NOT trip at the right current level to protect nominal 120V circuitry.  Something
like this  switch/fuseholdermight be appropriate.   Not sure  it's up to modern safety standards, though; my stove is old.


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## jonjeffl (Apr 9, 2022)

Stick with the NEC, A bit more work perhaps but always safe.


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