voltage drop ?

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electricblue

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I have a heat pump dropping voltage when running. 209 volts a disco. When it turns on goes down to 195. The manufacture said if not fixed they won't warranty the thing. They did install a 2nd capacitor. It's 41.1 minimum circuit, 50 feet from panel. Wired in #8. I think I'm in the clear. What do yall think? It's 208 service btw.
 
electricblue said:
I have a heat pump dropping voltage when running. 209 volts a disco. When it turns on goes down to 195. The manufacture said if not fixed they won't warranty the thing. They did install a 2nd capacitor. It's 41.1 minimum circuit, 50 feet from panel. Wired in #8. I think I'm in the clear. What do yall think? It's 208 service btw.
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The distance from the panel doesn't mean anything. How long is the cable run? Measure the current draw when the unit is running and then do a voltage drop calculation.

There are different possibilities.

The unit may be drawing more current than calculated at the factory ( bad unit).
There may be a loose connection.
That cable may be a lot longer than 50 ft.

Clear may mean you have a very unhappy customer.
 
growler said:
The distance from the panel doesn't mean anything. How long is the cable run? Measure the current draw when the unit is running and then do a voltage drop calculation.

There are different possibilities.

The unit may be drawing more current than calculated at the factory ( bad unit).
There may be a loose connection.
That cable may be a lot longer than 50 ft.

Clear may mean you have a very unhappy customer.
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Checked connections. Cable run is approx 50' to 60'
 
Using MCA only to try to determine VD is tricky. Do you know the actual RLA?

Does the equipment actually state a minimum voltage tolerance it can accept? Kind of CS for them to tell you AFTER the fact by threatening a voided warranty if you ask me.

Equipment voltage ratings are typically +-10%. 208V less 10% should be 187.2V minimum, so what's likely happening here is that they sold a 230V rated unit, which less 10% means it can handle 207V, which means you cannot handle even a 1% drop on a 208V system. That's going to be tough. Using #6 (and using 41.4A) ends up with a VD of 1.829V at 50ft., so your terminal voltage will be 207.17 (starting from 209V), barely within tolerance. Find out the actual RLA and do it from that to see if you make it with #8, might be tough.

http://www.southwire.com/support/voltage-drop-calculator.htm
 
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electricblue said:
MCA 41.4
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electricblue said:
Checked connections. Cable run is approx 50' to 60'
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Have to guess at the full load amps but useing something around 50 I just don't get that much of a voltage drop.

I would measure the current draw and see what the load is.


When you say heat pump are you taking about the condensor unit or the air handler? Is there a change ther is more load than you think?
 
If we assume only one motor, and MCA of 41.4A likely means a motor FLA of 33.12 (41.4 / 1.25).

1 conductors per phase utilizing a #8 Copper conductor will limit the voltage drop to 1.10% or less when supplying 33.12 amps for 50 feet on a 208 volt system.
For Engineering Information Only:
40.0 Amps Rated ampacity of selected conductor
0.7421 Ohms Resistance (Ohms per 1000 feet)
0.052 Ohms Reactance (Ohms per 1000 feet)
10.4 volts maximum allowable voltage drop at 5%
2.287. Actual voltage drop loss at 1.10% for the circuit
0.9 Power Factor
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Should be OK, unless they really can't handle more than a 0.5% VD (207/208V) as I suspect. So what I'm getting at is that the MCA value is likely based on 230V, or even worse, 240V. Then because you are feeding it 208V, you are outside of acceptable tolerances and all bets are off.
 
But still: why so much voltage drop unless there is already a bad connection somewhere or it's actually drawing way more amperage?


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Jraef said:
If we assume only one motor, and MCA of 41.4A likely means a motor FLA of 33.12 (41.4 / 1.25).



Should be OK, unless they really can't handle more than a 0.5% VD (207/208V) as I suspect. So what I'm getting at is that the MCA value is likely based on 230V, or even worse, 240V. Then because you are feeding it 208V, you are outside of acceptable tolerances and all bets are off.
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This is correct. A 208 motor is a 230v motor. Anything less then 208 needs a 200volt motor.
 
What does a amp clamp say the motor/equip is pulling?

I can't imagine 50-60ft of wire would drop any at all voltage wise.

Does the motor meg out good? Sound/feel good bearing wise?
 
took an amp reading 36.30 amp running. RLA 32.05 sticker Had 211.6v before running drops to 204v when compressor kick in and slowly comes up to 205v 206v. I thinking of pulling another pair of #8 and have 2 parallel 8's. I still think there is something else wrong.... Wiring issue in unit?
 
You're not allowed to parallel #8's (in most cases, you can only parallel 1/0 or lager conductors). You may need to repull #6's.

I'd measure voltage at the Service to make sure the power drop or transformer aren't a large part of your problem. If there's a feeder involved too, check its contribution.
 
suemarkp said:
You're not allowed to parallel #8's (in most cases, you can only parallel 1/0 or lager conductors). You may need to repull #6's.

I'd measure voltage at the Service to make sure the power drop or transformer aren't a large part of your problem. If there's a feeder involved too, check its contribution.
Click to expand...

Good idea! I'll check farther back.
 
I checked a automatic parts washer that wasn't working a while back. The voltage dropped to 200v at the machine when running.
It was 204v with the machine off.
Also 204-205v at the topside of the main disconnect out at the meter.
POCO problem. 120v/208 wye. 205v was the highest reading.

Usually a 120/208 wye will read 211 ~ 215ish across the phases.

The parts washer had a 240v to 120v control transformer, it was supplying 102v to the control circuit.

With the low voltage supplied to the building the 120v contactors were getting 102v and were hit and miss as to wether they would pull in or pop the 3a control fuse.

Check your power as soon after the transformer as possible to see what the POCO is actually supplying.
 
texie said:
50 feet from the "panel". What is the drop to the panel? The 50' may be the least of the VD.
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electricblue said:
211 at panel. 209 at disconnect
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Texie I believe is on the right path, you are looking for troubles further upstream - maybe even a POCO transformer that is not high enough capacity for the load it serves is already giving you low voltage, or a long service drop or lateral or feeder within your facility - you can change all you want in your circuit it will do nothing for what problems are upstream.
 
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