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Old 09-17-2009, 02:59 PM   #1
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New 240V receptacle reads zero volts


Hi All,

I'm installing a new receptacle for a table saw. It's a 15A 240V circuit on a 2-pole breaker with 14/3 wire. The saw draws 9A at 240V.

After installing the breaker I tested the receptacle. Each slot measured with ground reads 125V, but both slots together don't read 240. They read zero volts.

Here's how it's connected:

@Receptacle: the hots (red and black) are connected to the brass terminals. The neutral (white) is connected to the silver terminal. The ground (bare) is connected to ground. (I understand that since my saw requires no 120V circuit that I don't technically require the neutral, but I used it anyway. Eliminating it during subsequent troubleshooting made no difference.)

@Panel: the hots (red and black) are connected to the screw terminals of the breaker. The neutral (white) is connected to the neutral bus bar. The ground (bare) is connected to the ground bar.

I have done the following troubleshooting:


  1. used two separate multimeters for testing with the same results
  2. measured current at the bare wires, eliminating the receptacle
  3. replaced the breaker with a different double pole breaker
  4. replaced the breaker with two separate single pole breakers
  5. replaced the wire with fresh wire
  6. tried the power switch of the saw anyway at each possible opportunity
  7. tested the saw for continuity; it's fine
In each case I had the same result: 125V at each slot when measured separately by grounding, but 0V when both slots measured together.

I'm stumped; clearly there's something about 240V circuits that I don't understand. Can anyone offer a suggestion?

Thanks,
--Derek

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Old 09-17-2009, 03:04 PM   #2
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New 240V receptacle reads zero volts


Do you have a picture of the breaker?

Sounds like a tandem breaker & not a 240v breaker
Tandem pulls both hots from the same hot bus & can't be used for a 240v circuit


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Old 09-17-2009, 03:12 PM   #3
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New 240V receptacle reads zero volts


Quote:
Originally Posted by Scuba_Dave View Post
Do you have a picture of the breaker?

Sounds like a tandem breaker & not a 240v breaker
Tandem pulls both hots from the same hot bus & can't be used for a 240v circuit

I have one of these:



You can see more specs here:
http://www.westsidewholesale.com/two..._-na-_-na-_-na
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Old 09-17-2009, 03:16 PM   #4
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New 240V receptacle reads zero volts


Federal Pacific... EECK!
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Old 09-17-2009, 03:18 PM   #5
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New 240V receptacle reads zero volts


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Originally Posted by RxScram View Post
Federal Pacific... EECK!
Does FP have a bad reputation or something?
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Old 09-17-2009, 03:24 PM   #6
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New 240V receptacle reads zero volts


Quote:
Originally Posted by Madroaster View Post
......there's something about 240V circuits that I don't understand.......Derek
This Diagram should help.
Your meter is measuring V1 to V1 which equals 0 VAC


Derek, Measure the V1 to V2 voltage at the breaker
.
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New 240V receptacle reads zero volts-edison-service.jpg   New 240V receptacle reads zero volts-edison-service-2h.jpg  
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Last edited by PaliBob; 09-17-2009 at 03:57 PM. Reason: added V1 to V2 for clarification
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Old 09-17-2009, 03:25 PM   #7
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New 240V receptacle reads zero volts


Quote:
Originally Posted by Madroaster View Post
Does FP have a bad reputation or something?
You might say that. Check out this link for some more information...

http://www.inspect-ny.com/fpe/fpepanel.htm
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Old 09-17-2009, 03:31 PM   #8
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New 240V receptacle reads zero volts


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Originally Posted by RxScram View Post
You might say that. Check out this link for some more information...

http://www.inspect-ny.com/fpe/fpepanel.htm
Thanks for that. I was unaware of any of this. This panel came with the home and was installed 20 years ago. I'll do some reading.
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Old 09-17-2009, 03:34 PM   #9
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New 240V receptacle reads zero volts


Quote:
Originally Posted by PaliBob View Post
This Diagram should help.
Your meter is measuring V1 to V1 which equals 0 VAC

.
It does clarify. It is what I understood to be happening, but I hadn't seen a diagram of it.

However, I still don't understand my particular problem. With the quick responses so far I suspect I will soon.
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Old 09-17-2009, 04:04 PM   #10
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New 240V receptacle reads zero volts


Do you have any extra space in your panel ? If you do try moving breaker up or down a space sounds like you are on the same leg of the bus
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Old 09-17-2009, 04:14 PM   #11
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New 240V receptacle reads zero volts


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Originally Posted by 300zx View Post
Do you have any extra space in your panel ? If you do try moving breaker up or down a space sounds like you are on the same leg of the bus
That was the problem. Thanks a lot; I would never have come up with that. I didn't know that situation could exist. I'm off to find a schematic of a panel box to see how it all goes together.

--Derek
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Old 09-17-2009, 04:22 PM   #12
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New 240V receptacle reads zero volts


It's hard to tell from that picture of the breaker, but it looks like SD was right on. What you likely have is a tandem breaker. It allows you to connect two circuits in one breaker space. A 240V breaker would be 2-breakers wide so it could pull power from each leg. The tandem pulls wire from one leg and then splits it into 2 circuits. On the back of the breaker, does it have one slot or two slots for the hot bus bar?

What you probably have is something like


And what you need is something like


See the difference? (Note, these are _examples_ and not the specific breaker for your box)
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Old 09-17-2009, 04:32 PM   #13
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New 240V receptacle reads zero volts


I like there return policy:
Product Description

This hard-to-find circuit breaker manufactured by Federal Pacific (Federal Pioneer) is used to replace your burnt circuit breaker. With the precise sensitivity of Federal Pacific's patented Stab-Lok system, this breaker will quickly protect your home from possible electrical hazards.

Technical Specifications:
- Breaker Type: NA/ Two Pole/ 15 Amp
- Breaker Size: Thin
- Voltage: 120/240V AC
- Interrupt Rating: 10000 Ampere
- Condition: New
- Listings: CSA Certified

ALL Circuit Breakers are Final Sale. No returns allowed on this item.
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Old 09-17-2009, 05:16 PM   #14
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New 240V receptacle reads zero volts


Derek, Glad you have it analyzed
.
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New 240V receptacle reads zero volts-panel-1a.jpg  
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Last edited by PaliBob; 09-18-2009 at 11:43 AM. Reason: update dwg
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Old 09-17-2009, 07:15 PM   #15
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New 240V receptacle reads zero volts


Quote:
Originally Posted by PaliBob View Post
Derek, Glad you have it analyzed
.
The second diagram was clearer, as was your edit. I understand it properly now.

Is this the way most (all?) residential panels work?

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