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Old 12-18-2016, 07:20 PM   #1
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Default Splices and voltage drop

I tried to improve voltage drop in a 6 outlet circuit with no luck. The customer's complaint was that the 1500W heater, at the last outlet on the 15A circuit, was causing other stuff in the house to power down. Breaker was not tripping.

I put my 13A heat gun on the last outlet and indeed saw a 1.5V to 2.5V drop between each of the 6 outlets. The breaker output was 118.6V and the voltage at the last outlet was 108V

Since the 6 receptacles on this circuit were ancient and backstabbed, I thought I had a pretty good chance of improving the situation by pigtailing all 6 outlets.

I pigtailed them all but the voltage drop improvement was hardly noticeable.

Voltage drop calculators say I should see a drop of 1.97% at 13 amps for the 30 feet this circuit runs. However, I'm seeing more like 8.9%

Do the splices really drop this much voltage or am I missing something?
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Old 12-18-2016, 07:28 PM   #2
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Quote:
Originally Posted by swimmer View Post

I put my 13A heat gun on the last outlet and indeed saw a 1.5V to 2.5V drop between each of the 6 outlets. The breaker output was 118.6V and the voltage at the last outlet was 108V
Sounds like the last outlet's contacts are half fried !
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Old 12-18-2016, 07:29 PM   #3
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Did you check the voltage at each receptacle along the way while the heat gun was running? I'd be curious as to what the voltages were along the run.
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Old 12-18-2016, 07:38 PM   #4
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Nah, something doesn't add up. You're losing over 130W of heat in this circuit that's only 30' long? The splices/devices would be hot to the touch.

My first question is how sure are you of the circuit length?

How sure are you there are no other loads spliced on? Did you take current measurements at the breaker?

Did you try moving the space heater down the circuit measuring drop at each point the heater was plugged in?
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Old 12-18-2016, 07:39 PM   #5
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A run of 6 outlets plus the feed would usually be a lot more than 30'.
Usually min of 14' plug to plug. A lot more if you're going over
doors etc..
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Old 12-18-2016, 08:02 PM   #6
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What size conductor you are running on this circuit?

to get that much voltage drop ya gotta have 14 ga conductors in there.

If alum conductors the bet is off the table.,,,

Many older homes some case you have to check the ceiling lumaires for loose connection up there .,, that how I found couple like that.
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Old 12-18-2016, 08:05 PM   #7
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The wire for this circuit is 14AWG.
It is about 30 feet max to walk from the panel to the last outlet but I suppose the cable length is much longer.
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Old 12-18-2016, 08:08 PM   #8
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Quote:
Originally Posted by hardworkingstiff View Post
Did you check the voltage at each receptacle along the way while the heat gun was running? I'd be curious as to what the voltages were along the run.

With the 13A heat gun in the last outlet, there is approx 1.0 to 2.5 voltage drop between outlets as you walk from the panel towards the last outlet
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Old 12-18-2016, 08:12 PM   #9
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FWIW, you can check the voltage to ground to confirm that it is really related to wire length. The voltage change in neutral and in hot should be nearly identical if what you are seeing is really resistive drop in the wires.

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Old 12-18-2016, 08:14 PM   #10
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Quote:
Originally Posted by swimmer View Post
The wire for this circuit is 14AWG.
It is about 30 feet max to walk from the panel to the last outlet but I suppose the cable length is much longer.
there is something is not adding up right with that much voltage drop as I expected for 14 ga conductors .,,

is this one of older copper cladded conductors ? if so that do fall in same rules with alum conductors.,,

but you should try at half point and disconnect anything else down stream and run a test to see how much voltage it drop with 13 Amp load on it.,,,

it should not drop very much just few volts which I do expected on 14 gauge conductors.,,
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Old 12-18-2016, 08:32 PM   #11
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vd = 2kil/kcmil = 2*12.9*13*l/6530


2.5 = 2 * 12.9 * 13 * l/6530

solving for l (the distance)

l=48' between receptacles (if I did the math right)


since you said you had approx 8' between receptacles,
the resistance seems to be 6x what it should be.
are the conductors severely degraded/corroded at the
splices (high resistance connection ?)

also might want to check my math (been a while since I used
that forumula)
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Old 12-18-2016, 11:53 PM   #12
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Wild guess here, check the neutral connection at the panel.

Is it a multi-wire circuit?
Does this happen to any other circuits in the home?
Does the voltage drop at the panel also? If so, does it go up at the same rate on the opposite phase?

I once had a section of BX disintegrate in the crawl space between two outlets which made a similar result happen. I had to install new wiring to correct it.
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Old 12-19-2016, 10:31 AM   #13
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Quote:
Originally Posted by wildleg View Post
vd = 2kil/kcmil = 2*12.9*13*l/6530


2.5 = 2 * 12.9 * 13 * l/6530

solving for l (the distance)

l=48' between receptacles (if I did the math right)


since you said you had approx 8' between receptacles,
the resistance seems to be 6x what it should be.
are the conductors severely degraded/corroded at the
splices (high resistance connection ?)

also might want to check my math (been a while since I used
that forumula)
Chap 9 Table 8 of the NEC lists the circular mils of #14 copper as 4110. I'm not sure where you got 6530.
So L = (4110 * 2.5)/(2*12.9*13) = 30.64 ft.
I don't usually do this without carefully listing units but I followed the example on http://www.mikeholt.com/technnical-v...s-part-one.php and got the same results.
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Old 12-19-2016, 10:39 AM   #14
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I must have been using the online voltage drop calculators incorrectly yesterday.
I used 3 different calculators today and used the formula Vd = 2*K*Q*Amps*D/CM
Vd is in volts
K = 12.9 ohms
Q is approx 1.0 for conductors smaller than 1 AWG
Amps = 13A
CM = 4110 (Chap 9 Table 8)

Solving for distance, the formula and the calculators all give a approx 8% drop for approx 125 ft. As has been noted, 30 feet from the the panel to the far bedroom could use 125 ft. of cable.

So 8% voltage drop for 13A on 125 ft of 14AWG cable is to be expected
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Old 12-19-2016, 11:17 AM   #15
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Quote:
Originally Posted by swimmer View Post
I must have been using the online voltage drop calculators incorrectly yesterday.
I used 3 different calculators today and used the formula Vd = 2*K*Q*Amps*D/CM
Vd is in volts
K = 12.9 ohms
Q is approx 1.0 for conductors smaller than 1 AWG
Amps = 13A
CM = 4110 (Chap 9 Table 8)

Solving for distance, the formula and the calculators all give a approx 8% drop for approx 125 ft. As has been noted, 30 feet from the the panel to the far bedroom could use 125 ft. of cable.

So 8% voltage drop for 13A on 125 ft of 14AWG cable is to be expected
Coincidentally the CEC/OESC now requires #12 for lengths
exceeding 38m, which is almost exactly 125ft.
Code ref Table 68
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Old 12-19-2016, 11:46 AM   #16
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Quote:
Originally Posted by swimmer View Post
Chap 9 Table 8 of the NEC lists the circular mils of #14 copper as 4110. I'm not sure where you got 6530.
So L = (4110 * 2.5)/(2*12.9*13) = 30.64 ft.
I don't usually do this without carefully listing units but I followed the example on http://www.mikeholt.com/technnical-v...s-part-one.php and got the same results.
I think I used the value for #12. like I said, it's been a while.
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Old 12-19-2016, 01:36 PM   #17
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The current can be (partially) choked at the circuit breaker, too.

FOP, anyone ?

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Old 12-19-2016, 09:28 PM   #18
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Quote:
Originally Posted by swimmer View Post
I tried to improve voltage drop in a 6 outlet circuit with no luck. The customer's complaint was that the 1500W heater, at the last outlet on the 15A circuit, was causing other stuff in the house to power down. Breaker was not tripping.

>snip<

Do the splices really drop this much voltage or am I missing something?
What other "stuff" powers down when this load is on? Is it stuff on the same circuit or other circuits?

And what exactly does the customer mean by "powers down?"

Have you told the customer running a 1500 watt load on a circuit with an 1800 watt limit is, while technically OK, pushing the limits of the circuit? (IMHO electric space heaters over 1000w should require either a dedicated 15a or 20a circuit)

I live right down the block from a railroad track with an electrically heated switch track - in the winter the thing must cycle on and off because my lights noticeably dim, and the UPS for my computer room would signal an under voltage alarm.

In the summer I'd sit outside on the back porch with the porch lights dimmed down, and whenever the refrig or an air conditioner would kick on, there is a noticeable dip in the porch lights. This is all perfectly normal.
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