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macebobo
07-03-2011, 04:11 PM
In my back yard, I have an old 240v circuit that at one time had a hot tub connected to it. What I would like to know is, if I take one of the two hot lines, neutral and ground to one outlet, can I do the same with the other hot, use the same neutral and ground and have two 120v circuits? Or, am I missing something?

Thanks,
John

somtng4u2c
07-03-2011, 04:19 PM
That will work

Mactayl
07-03-2011, 04:25 PM
In my back yard, I have an old 240v circuit that at one time had a hot tub connected to it. What I would like to know is, if I take one of the two hot lines, neutral and ground to one outlet, can I do the same with the other hot, use the same neutral and ground and have two 120v circuits? Or, am I missing something?

Thanks,
John

No you are not missing anything, most homes are split 240V but the outlets are usually laid out so they are not close together because there is a 240volt potential if you have the outlets side by side and that can very dangerous.

Materdaddy
07-03-2011, 04:28 PM
In my back yard, I have an old 240v circuit that at one time had a hot tub connected to it. What I would like to know is, if I take one of the two hot lines, neutral and ground to one outlet, can I do the same with the other hot, use the same neutral and ground and have two 120v circuits? Or, am I missing something?

Thanks,
John

I *just* had the same situation. As far as I know, you cannot do what you describe, unless you cut your capacity up strangely. If you have a wire gauge capable of 30 amps, and you ran two 30-amp circuits that shared a neutral, think about having 20 amps pulled through both circuits. The hots would be fine and the breakers would not trip, but you'd have 40 amps going through that neutral.

You can use the ground and have 2 un-grounded circuits, but I don't think that's wise either. I think the best bet is to do what I did and waste 1 wire. I have one 110 circuit out there and waste 1 wire.

glaforce
07-03-2011, 05:16 PM
I may be wrong but i thank its common place (and ok by NEC) to have a common neutral for upto maybe 5 devices. Someone people say if thats wrong. I dont what to give the wrong advice however i see no issue with spliting the 240vac connection the way stated above.

StandingInAwe85
07-03-2011, 05:33 PM
I *just* had the same situation. As far as I know, you cannot do what you describe, unless you cut your capacity up strangely. If you have a wire gauge capable of 30 amps, and you ran two 30-amp circuits that shared a neutral, think about having 20 amps pulled through both circuits. The hots would be fine and the breakers would not trip, but you'd have 40 amps going through that neutral.

You can use the ground and have 2 un-grounded circuits, but I don't think that's wise either. I think the best bet is to do what I did and waste 1 wire. I have one 110 circuit out there and waste 1 wire.

I could be mistaken (so someone please confirm or deny this), but I always thought the current on the neutral would be the difference between the two hots. So having one 120v circuit pulling 20A and the other at 15A would only put about 5A on the neutral, not 35A.

Also, you may want to check the breaker you have on that line. Most 240V circuits use a double-pole breaker. You might be able to switch that to two single-pole breakers (probably should use 20A breakers to be safe).

Materdaddy
07-03-2011, 06:08 PM
I could be mistaken (so someone please confirm or deny this), but I always thought the current on the neutral would be the difference between the two hots. So having one 120v circuit pulling 20A and the other at 15A would only put about 5A on the neutral, not 35A.

Also, you may want to check the breaker you have on that line. Most 240V circuits use a double-pole breaker. You might be able to switch that to two single-pole breakers (probably should use 20A breakers to be safe).

After doing some more reading, it seems this might be correct as long as you are sure the two hot lines are on different legs in the main breaker. That means the two sine waves are 180* out of sync and the neutral will only carry the difference as you stated.

I went the "safe" route that I understand since I didn't hire an electrician for the work.

JonB256
07-03-2011, 11:06 PM
A hot tub power supply will be wired back to a single 2-phase breaker. Because the two Hots are 180 degrees out of phase, the neutral current will not be a problem. In fact, if you pulled 18 amps on one phase and 17 amps on the other, the neutral current will only be 1 amp. If you balance the sides perfectly, there will be ZERO neutral current.

As a side note, some 240V home appliances only have three wires (2 hots and the ground) because they balance the load so closely. Stoves and clothes dryers and water heaters, particularly.

macebobo
07-04-2011, 01:46 AM
Thanks everyone. When I took off the cover of the panel, I was shocked to see the mess. We live in a 136 year old house, so there has been some changes with time. The hot tub breaker was on a double pole 50 amp breaker. The wire was 6g, 3 conductor wire. That's right, zero grounding! :o Needless, to say, I skipped using this wire. I will probably rip that wire out and use a proper setup if I want power in the back yard. I did see that I had space and capacity for 5 more breakers :D

But while I was in there, I saw that a 70 amp circuit had the hots pulled out and capped with wire nuts. I thought to myself, maybe those go to the garage breaker box, since I had tested it earlier and it was dead. Sure enough! I now have a dedicated 70 amp, breaker controlled box for blinky flashy in the garage, with a conveniently located pet door just beneath :D

Wish I had pulled that panel off last year!

-- John

n1ist
07-05-2011, 08:02 AM
Just to clear up a few points (BTW, I'm not an electician, so check with a licensed electrician before proceeding). Some of these notes are generic, not specific to this installation.

- If you have a neutral present (white wire), you can create a multi-wire circuit and split it into 120V circuits. Note that each hot must be fed from a different phase, and (if you are in an area that follows the most recent NEC), must be fed by a
multi-pole breaker or breakers connected by handle ties.

- If you don't have a neutral (just 2 hots and a ground), you can convert it to a single 120V circuit. You may run into code issues with reidentifying a wire thinner than #6 as a neutral, but I don't have a code book handy.

- NEC does allow you to have the receptacles on different phases in the same box; you can even split a duplex receptacle with one phase feeding each half (don't forget to break off the connecting tab)

- Unless you have two legs of a 3-phase circuit (in which case you would measure 208v between the hots, not 240v), the neutral will carry the imbalance. For two hots of a 3-phase, there's a square root of 3 in there somewhere, so it doesn't totally cancel like it would if you were using all three phases.

- You can NOT connect 20A or 15A receptacles directly to a 30A or higher circuit. You either need a subpanel or need to replace the feeding breaker with a 20A one.

- If the circuit is feeding another structure (detached garage, box on a post in the yard), you may need to have ground rods at the structure. The NEC also specifies depth that wires or conduits need to be buried at.

/mike

Materdaddy
07-05-2011, 09:54 AM
http://science.howstuffworks.com/environmental/energy/power.htm

That's a really good article that explains a lot. Including that houses only get 1 phase of power with a center tap of the transformer as the neutral. That is how you get 240v, 120 either side, so I believe there is no square root of 3, it's not 120* out of phase like 3-phase power, it's actually only 1 phase, 180* rotated because of the center tap of the transformer.

As everybody else has stated, check with a licensed electrician to be sure!

n1ist
07-05-2011, 02:23 PM
Some large apartment buildings and complexes are fed with 3-phase, and drop 2 phases to each unit. Heating appliances won't get as hot as they are fed with 208 rather than 240. It would also confuse some of our gear that gets zero-crossing from one input and assumes the other side is the same.

As Materdaddy points out, most of us get a single-phase centertapped transformer feed, with 2 hots 180 degrees out of phase, so the neutral does get the difference in a multiwire circuit.
/mike

Materdaddy
07-05-2011, 03:24 PM
Some large apartment buildings and complexes are fed with 3-phase, and drop 2 phases to each unit. Heating appliances won't get as hot as they are fed with 208 rather than 240. It would also confuse some of our gear that gets zero-crossing from one input and assumes the other side is the same.

As Materdaddy points out, most of us get a single-phase centertapped transformer feed, with 2 hots 180 degrees out of phase, so the neutral does get the difference in a multiwire circuit.
/mike

I don't live in an apartment or large complex, but I'm curious if there's an easy way to tell if your service has 2 of the 3 phases of 3-phase power, or if you have 1 phase that is center tapped?

IdunBenhad
07-05-2011, 07:13 PM
Hi:
I am not an electrician, although I have done considerable electrical wiring, including an entire house with NO rejections from a state inspector. Electronics is what I've done all my working life.

So, if I'm missing somethng here, please 'splain' that to me.

If there is a center-tapped transformer fed circuit with 120 vac on each side of the center tap and 180 degrees out of phase, how is that there is no current in the neutral lead (center tap)? There has to be a return circuit for the current, whether it be the neutral lead (center tap) or ground and all current must flow through that circuit.

There cannot be zero return current. This would happen only in an open circuit. The return currents do not cancel each other out. So, if there is 17 amps on one side and 18 amps on the other, the resultant return current is Not 1 amp. It is 17 amps on one side and 18 amps on the other. They just do not occur simultenously.

Straighten me out, please.

StandingInAwe85
07-05-2011, 08:12 PM
Hi:
I am not an electrician, although I have done considerable electrical wiring, including an entire house with NO rejections from a state inspector. Electronics is what I've done all my working life.

So, if I'm missing somethng here, please 'splain' that to me.

If there is a center-tapped transformer fed circuit with 120 vac on each side of the center tap and 180 degrees out of phase, how is that there is no current in the neutral lead (center tap)? There has to be a return circuit for the current, whether it be the neutral lead (center tap) or ground and all current must flow through that circuit.

There cannot be zero return current. This would happen only in an open circuit. The return currents do not cancel each other out. So, if there is 17 amps on one side and 18 amps on the other, the resultant return current is Not 1 amp. It is 17 amps on one side and 18 amps on the other. They just do not occur simultenously.

Straighten me out, please.

If this were DC current, you would be correct. I have an analogy I like to use to try and understand AC current in applications like this. I like to imagine that each wire that comes into the house is a water pipe. On the two hot pipes, imagine that the water isn't flowing like a typical water pipe, but rather being pushed out and then sucked back in, and then pushed out, and then back in, and so forth. The two hot pipes would be the opposite of each other, so when one pipe is pushing the other is sucking. Now, if both pipes were pushing exactly the same amount of water at all times, things would be great. However, this isn't going to be the case in home applications, therefore we need a neutral pipe to take care of the surplus, and then lack of, water. Since both pipes are tied together (on the "neutral" bus in the breaker box after the current goes through the load), they will take care of a majority of the flow and thus the neutral (which neither pushes or sucks on its own) should only take a small part of the load. Hope this helps (and is at least a generally accurate analogy).

Materdaddy
07-05-2011, 08:26 PM
This is what I read to understand... maybe it's too simple?

http://forums.mikeholt.com/showthread.php/89023-Help-understanding-neutral-conductor.?p=708650#post708650

mkess
07-11-2011, 04:26 PM
Why dont you just put a subpanel where the wires are stubbed through? Then you can break it down into separate circuits. If you are worried about the grounding issue, first check your main panel if you neutral and ground are tied together you are good to go. If not then all you would need to do is drive a ground rod underneath your sub panel and connect your ground wire from subpanel to it.

g2ktcf
07-11-2011, 04:55 PM
I have a 30A Dryer Circuit that I am planning on making into a portable subpanel

wwwgator
11-02-2011, 03:52 AM
Getting caught up on posts.....stumbled across this....

I am a Master Electrician and an inspector, so I thought I should chime in.

Yes, you can covert an old hot tub (3 wire +ground) to 2 -120V circuits.
you need to do the following:

remove the 50-70A GFCI breaker (sell it on ebay). land the neutral on the neutral bar. Land the 2 hot wires on a 2 pole breaker (required for networked circuits)
a QO220 (Square D) or CH220 (Cutler hammer) The design of these devices automatically sets the phasing (L1- L2).
At the local disconnect (where the hot tub was connected to- you will have to splice #12 awg onto the the #6awg as the 20A recepticle wont take that large of wire.
Use GFCI recepts. as the outlets are outside (required by code) and use "in use" covers to protect the device(s)

If you have any doubt, call a local electrician, or PM me.

Above all, be safe.
This isnt rocket surgury, but it is dangerous.