Hello, I want to install new circuits in my basement and I want to do it off of an electrical sub panel. The subs i see are only 1 phase. How to I tap into the main box? Do i still use a double pole breaker? Single pole breakers only go upto 30 amps. I want to run 4 separate circuits off the new box. Thanks.
I had the same idea to power a tankless water heater but found it better for My place to upgrade to a larger,higher amp panel.. Members here might need more info as to what Your existing set-up is to give You the best help;;What amp is the main in Your box? Is the existing panel full or are there unused circuits? Are You adding 15 amp circuits? 20 amp? larger? What amp is the service from the meter outdoors? Do You have specific uses in mind for the new circuits so the amp draw can be estimated or just general use? I'm not a Sparkie but am interested after My recent upgrades.. Dean
As Dean said, you need to furnish a lot more info. When you say that subs you see are only 1 phase, you're correct, it's rare for a residential service to have 3 phase. Are you looking to connect a machine that requires
3 phase or just not familiar with the terminology? You will need to know the size of the existing service and some idea of what's attached to it currently. You'll also need to provide details of what you're looking to connect in the basement, to determine the feeder and panel size. BTW single pole breakers do come in larger than 30 amp, however its usually more practical to build the device to operate at 240 volt and keep the amperage lower
OP-
I believe you mean "legs" ..........or do you really mean phases...????
I suggest using a Square D QO Load Center..the one I'm thinking of has
8 breaker slots (100 or 125 amp rating; I think) & is feed 220V ( 2 legs) via a double pole breaker from the main.Now you have sub panel that is mini version of your main...two legs, across which you have 220V when you use a double pole breaker.
If you really mean phases & you're trying to get 3 phase power out of a residential service you're sol unless you buy a phase converter.
but I'm pretty sure the first part of my answer will get the job done for you, since it seems like you're just looking for more amps for a heavier drawing load....and the way to get that is on a 220v circuit.
cheers Bob
Actually most sub panels do use 2 hot legs (240v and 120v), don't confuse that with the term, "single phase". That is really one "phase", center tapped to give you two 120v circuits. You use a 2 pole breaker in the main panel and be sure to run a 4 wire feeder to the sub. Buy the extra ground bus kit. Leave the bonding screw off the neutral bar, connected to the white wire in the fereder and it stays insulated. The bare/green wire in the feeder goes to the supplimental bar and that is where your ground wires go.
When I meet up with a person who wants put in a sub, I quickly ask why?
There might be better solutions. Now since you said you want more circuits, has a service calc been done?
tom @
It can be one phase or two, depending on your reference point. However, either way it's not three.
Step one: For just 4 circuits, you'd be better off just home running all 4 back to the main panel. Lots less hassle and discussion. If you're out of room on the main panel, then put the sub panel right next to the main and see step one.
This is still singe phase. The fact that it is center tapped does not add a phase. "Two phase" does exist but most people will never see it. That has the phases shifted by 90 degrees and uses 4 circuit conductors..
Making that center tap the reference point (which seems logical since it's grounded) and examining the voltages on the other 2 conductors, you now have 2 points out of phase with other. 2 phases.
I even looked up the definition of "phase" again. Nothing about it excludes 180-degree separation.
I haven't really seen it, but have read about it.
That's definitely 2 phase. That does not limit "2 phase" to that. That would be like saying that the definition of "money" is "$15" (allowing no other amounts to qualify).
There's also 4-phase, and I have seen that but only for driving stepper motors.
As previously posted 2 phase power is very rare now days. Typical service panels are a 3 wire single phase system. It is very common to incorrectly refer to this as "two phase". Follow the link for an explanation.
Leaving out the important words that you are referring to a PARTICULAR
2-phase system.
That does SAY that, but fails to consider that the word "phase" already has a meaning.
BTW, what definition of "phase" are you using?
I'm noticing the parts of my post that you ignored.
I suppose you can call single phase AC two phase you want but it will only tag you as an amateur around electrical professionals.
Of course it has NOTHING to do with what I want. It has to do with what the WORD "phase" actually means.
BTW, I never said I don't call it "split phase". I just said it was 2 phase also.
Just to be sure we're still talking about the same thing, it's AC from a center-tapped transformer secondary with the center tap grounded?
Are you using a definition of "phase" that DOESN'T apply to the
120/240VAC electrical system? What it that definition?BTW, here is one definition:
*********************************************************Source: American Heritage Science Dictionary (c) 2002
Of course it's a lot easier to understand than to explain.
AC is definitely "cyclic behavior", and when you examine the 2 nongrounded conductors at he same time you see the cycle at 2 different points. You can measure the voltage between the HOT wires of
2 different 120V outlets (120V hot to neutral). You get either 0V or 240V. That's enough to tell you something's going on. 120V is not the same as 120V (measured at different outlets). What's different about it?All that sounds fine, however when you are referring to residential and commercial electrical services in the US, they are generally referred to as single phase and three phase
Yes they are. I was never arguing about that.
There is only one secondary winding so it is single phase. The center tap does not change that.
I think the main problem may be that there is also a "two phase" power system which uses two phases separated by 90 degrees. It is no longer common in power distribution as it has been replaced by 3 phase systems but is still used in specialized applications.
The center tapped system is included in the category of "single phase power" but you do hear even electricians refer to "the other phase" or "the opposite phase". It is even weirder when you have a three phase delta system with one side center-tapped and grounded. It is one of those unfortunately ambigious situations where the language is sometimes not precise enough to clearly describe the situation. People have been disagreeing and arguing this point forever and probably will continue forever. It is not a disagreement about the facts, but only "What is the nameof it?".
Don Young
Yes, there is one winding. That doesn't keep the reference point (for measuring voltages) from being in the middle (center tap), and different phases being measurable depending on which end of that winding you measure at.
The center tap is actually in the center, meaning the voltage will be the same which ever end you measure. What is different if not phase? If nothing was different, you could put a wire between those points (the ends of the winding) and have no current flow (so your 240V appliances couldn't be working).
Right.
I'd find that 3-phase delta system confusing too.
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