Latest Discussions : Electrical & Lighting


04:24PM | 04/09/07
Member Since: 11/01/06
34 lifetime posts

I just bought a central vacuum. I need to put a 15A breaker. The unit works on 220/240v. The plug that I have is nema 6-15r.

My load center has come empty slots. I went to HomeDepot and bought a 120/240v circuit breaker. If i put it into the load center, how ill the vacuum know that it is indeed 220v?


Tom O

04:12AM | 04/10/07
Member Since: 09/17/02
476 lifetime posts
If that breaker has 2 places to connect wires, then it is for 240 volt circuits and you have the correct breaker.

The 120/240 volt rating means that the breaker can be used on circuits where no conductor exceeds 120 volts to ground and the voltage between any two conductors does not exceed 240 volts.


09:04AM | 04/10/07
Member Since: 04/25/05
1915 lifetime posts
It took me a while to figure out what your question is.

The breaker is a 2 pole breaker. That is one pole for each leg of the split 120/240 electrical supply.

The service is setup so that each leg is 120 volts from the hot to the neutral and 240 from one hot leg to the other.

For loads such as that vac or air condictioning compressors the load is only 240 volts.

So a hot wire is run to each breaker, plus a 3rd wire for the ground.

Some equipment (mostly dryers and stoves) are both 120 and 240 volt loads. They require runing 4 wires (for new circuits). The 2 hots and a neutral for the 120 and the 4th is the ground.


08:20AM | 04/11/07
Member Since: 11/01/06
34 lifetime posts
thanks for the answers guys!

The load center is a Square-D and the Breaker is a QOT1515. It is a twin breaker with 2 times 15A (there are indeed 2 prongs moving individualy). I think they call this a twin breaker for saving space in the load center.

I understand the principle: the rule of thumb is if the breaker has 2 poles, it's 240v. if it has only 1 pole, it is 120v.

I am not talking about the special breakers for 30A or 40A...

Am I right in assuming this?

Thanks again! You are just a great bunch of people here!


09:32AM | 04/11/07
Member Since: 04/25/05
1915 lifetime posts
The tandem break is two breakers on a single leg of the 120/240. The difference between the 2 terminal is ZERO and it can't be used to supply a 240 load. It only have one connection to the bus bar.

For 240 loads you need a 2 pole breaker.

It will be double wide. Some brands have one common handle. Other have two handles and a factory tie bar tying them together. It has 2 connections to the bus bar. And you can get 240 connecting between the two terminals and 120 from one terminal on the breaker and the neutral.

Here is the 2 pole version.

There is also what is called a quad breaker. It consists of 2 tandem breaker side by side.

It appears that there is none in the QO series, but you can assemble one.

Look down almost at the bottom and find "QOT Tandem Circuit Breakers"

And this note "Order two QOT1515 or QOT2020 circuit breakers and handle tie

Cat. No. QOTHT at $2.50 for common switching of center two poles"

Thsi shows how they are used.

When doing this the two inter breakers are on different legs and you have 240 between them.

This are usefull when you have full panel and can beplace 2 single pole breakers with 2 tandems. The existing 120 loads are connected to the 2 outer termimals and the 240 to the inter two termimals and the tie bar is used on the inner two handles.

NOTE - tandems can only be installed in certain slots as shown on the panel and not all panels will accept them.

Tom O

11:43AM | 04/11/07
Member Since: 09/17/02
476 lifetime posts
I knew I'd get in trouble by taking the easy way out and not properly describing a 2 pole breaker.

Square D's stock number for the breaker you need is QO215.

If you don't have the space needed for this breaker(two full spaces) you'll have to follow Bill's advice & assemble your own tandem breaker as he outlined. If you go that route, don't be tempted to make your own handle tie, use the factory made one.


12:44PM | 04/11/07
Member Since: 11/01/06
34 lifetime posts
ok ok ok ok !

I'm lost here!

Q1. Is the QOT1515 the right choice for running my vacuum? If not, I was under the impression that the 1515 was for 15A 15A so in my mind OK for the vac...

Q2. If the QOT1515 is *NOT* the right breaker, which one should I use?

I'm lost... and I'm not on an island! LOL

Thanks for all your help... and most of all... your patience with me! ;)


03:40PM | 04/11/07
Member Since: 04/25/05
1915 lifetime posts

It takes two full slots.

I suggest that you stop by the library and look at a book or two on wiring and see how 240 circuits are wired.

Look at how an AC is wired.


04:05PM | 04/11/07
Member Since: 11/01/06
34 lifetime posts
Thanks for all your hints!

I did wire the stove... from the load center to the wall outlet and it was so easy to choose the right breaker!

now... i'll go back to HD and buy a new breaker as mentioned.

But regarding the QOT1515... what are they used for? WHat's the difference between a 'tandem' breaker and a regular breaker?

Many many thanks! ;)


05:31PM | 04/11/07
Member Since: 04/25/05
1915 lifetime posts
Tandem breakers are just two independent breakers that will go in one slot.

Some panels need them to full usages.

For example some panels are label 30/40. That means that they have 30 slots, but if you use tandems in 10 of the slots then you can have 40 different poles (ie, 40 different 120 volt circuits).


06:32AM | 04/12/07
Member Since: 11/01/06
34 lifetime posts
if i were to remove 2 single pole breakers from my load center and replace it with 2 tandems... i would have 4 breakers for the price of 2 and i could connect all wires from those 2 breakers and fit them to the 2 tandems... beacuse if this is the case... i'll gladly do so... in no time!

thanks again!


09:11AM | 04/12/07
Member Since: 04/25/05
1915 lifetime posts
Well I don't know the prices of the different breakers but I suspect that tandems are a little more than a single breaker, but might be a little less than a 2 pole.

But you need the tie bar. Doubt if you will find that at a Lowes or HD. Probably need to go to an electrical supply house.

And the panel has ben able to accept tandems in that particular slots. Some panels won't accept them at all and others only in certain slots.


07:25AM | 04/26/07
Member Since: 11/01/06
34 lifetime posts
Hi again Bill,

It is only today that I can finally plug everything in order to make my central vac work.

I have bought a 15A breaker. Now since I have added the breaker in my LC, I checked the other 240v breakers (range oven, dryer)... and they have 3 wires... red - black - white (and gound).

The I have bought heatex cable (red envelope black and red wire plus ground).

In order to connect the central vac, don't I need a 3 wire cable like the oven and dryer? If not, which color wire goes to which pole on the breaker?

Thanks for all your info and PATIENCE!



08:04AM | 04/26/07
Member Since: 04/25/05
1915 lifetime posts
I had never heard of this.

But found it.

It appears to be NM (sheathed electrical cable) with with with a different color scheme.

In the US the common practice is to use regular NM and remark the white wire with tape or marked.

The stove and dryer are 240/120 volt devices. They use both voltages and require a neutral.

The vacum (and like heaters and AC units) only use 240.

Thus the red and black connect to the two breaker terminals and to the 2 hot (brass) terminals on the receptacle.

The bare or green to the ground bus.


05:35PM | 04/26/07
Member Since: 11/01/06
34 lifetime posts
guess what Billhart...


you've guided me through all this and THANKS TO YOU... IT ALL WORKS!

many MANY thanks!


03:40PM | 05/22/10
Member Since: 05/21/10
1 lifetime posts
I believe I'm caught up in the same question as you had a few years ago -- I need to put in some 240v outlets and was looking at the QOT1515 breaker as a means to run the circuit -- the confusing part was because Square D listed it as a 120/240 voltage rating (which, really, does that make sense?) -- anyway - I think the only answer is to consider buying a while load of QOT1515 to save some space and then put in some QO215's where I need 240v circuits...

Any further advise you can share from your experience is very much appreciated though...


06:44PM | 05/22/10
Member Since: 01/09/07
199 lifetime posts
Yes, a normal 240 circuit breaker has to be a double one, taking up 2 slots in the box. (That's how it connects to 2 sides to get 240V.)

If your box is full, this may indeed require replacing some current single breakers with the tandem ones, to free up enough space for the double 240V breaker.


06:11AM | 05/20/13
It's safe to bet the panel only has enough room for a certain amount of phased breakers. You could use them all to give 100 amp sub-panels. You shouldn't be experiencing any tripping. Freeing up enough space for that new square d circuit breaker you bought is tedious but worth it in the long run.

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