5% voltage drop on 240 volt heater start up

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AC\DC

Senior Member
Location
Florence,Oregon,Lane
Occupation
EC
Customer installed complete floor heat for house. Unit when turns on draws little under 40 amps. When unit comes on voltage drops from 243 to 230v ,Tad over 5%.
Does not seem right. I have to check the reading from meter main, and see if I get that out there. Only reason we found out was fan fire fireplace when I fixed he noticed it would bob down, till heat turned off.

Normally I am use to finding lose neutral, but since this is straight 240 load wondering and if meter main side is good, that power company wire is undersized or bad connection on line side some were. There run is about 300-400 feet.
Going to draw it out and try some math.
 
The good news about an electric heater with excessive (?) voltage drop -- all that excess is converted to heat.
Of course, that doesn't help much if it's the power company's feeder. But if it is, at least you're not paying them for heating the Great Outdoors.
 
AC\DC said:
Normally I am use to finding lose neutral, but since this is straight 240 load wondering and if meter main side is good, that power company wire is undersized or bad connection on line side some were. There run is about 300-400 feet.
Click to expand...
Even though this issue does not involve the neutral, making L-N voltage measurements in addition to L-L ones at the meter main may help diagnose the root cause of the problem.
A suggestion is to first turn off the L-N loads or at least confirm that the total current on the neutral bus is relatively small. That way the voltage drop along the neutral service conductor should be negligible, and so you can use it as a good reference point for measurements. Then you can check whether there's a larger L-N voltage drop on one phase than the other when the floor heater is turned on, which would indicate that there's probably a bad connection on that phase. If the L-N voltage drop occurring when the heater turns on is about the same for both phases, then it's more likely that the service run is undersized vs. having an equally bad connection on each phase.
 
211023-1123 EDT

AC\DC:

Where is the voltage measured? 243 to 230 is a 13 V drop at 40 A, or about 0.33 ohms of source impedance before the point of voltage measurement. For 40 A you would want #8, and at 20 C this is 0.628 ohms per 1000 ft. So 0.33 ohms is about 525 ft of loop length or 263 ft one way.

At my home and with a 12 A load at 120 V I get about 1 V loop drop from the power company service lines. Or a loop resistance of about 0.084 ohms.

2.93 kWH = 10,000 BTU.
230 * 40 = 9.2 kW.
9.2/2.93 = 3.14 .

10 kW seems low to heat a home, unless you are in the deep south. And Oregon is not deep south.

So a continuous on 9.2 kW for 1 hour will produce 31,400 BTU per hour.

My two gas furnaces can produce somewhat over 200,000 BTU per hour. The design criteria is to maintain 70 F at -20 F. This is almost a 100 F change. At 30 F outside I run near a 50% duty cycle.

See my plots at http://beta-a2.com/wire-1_photo.html

You need to measure no load voltage line-to-line at the main panel input lugs, then with the 40A load on. Do the same measurements at the load.

.
 
They have a wood fireplace for main heat.
They have 4 separate 20 amp circuits all on contractors with one single thermostats.
no load is 243 L-L 121/122 L-N roughly.
When heater kicks on L-L drops to 230 and L-N drops same percentage 114/116 roughly.
Sorry I did not include that. Seems it power company service undersize but I only checked at panel in house. Meter main is about 100 feet away.
 
211023-1931 EDT

AC/DC:

I believe the demark point for the power company is the meter. Your panel ( where I believe you are measuring voltage ) is 100 ft from the meter.

13 V drop at 243 V is a 5.35 % drop at your measuring point. Some of this drop will be before the meter.

My guess is that you have less than 5 % drop from the meter to the main panel.

Using the figures I mentioned for my home, and considering a 240 V source, then at 200 A I get a 7 % drop for my home..

I would judge that you do not have excessive voltage drop by allowed rules. See if you can determine loop wires resistance from the meter to your measurement point. Then see what calculations tell you. Who owns the wire from the meter to the home?

.
 
300-400’ is excessive. What size is the aluminum service
 
AC\DC said:
Customer installed complete floor heat for house. Unit when turns on draws little under 40 amps. When unit comes on voltage drops from 243 to 230v ,Tad over 5%.
Click to expand...
You didn't say what the service size is but I wouldn't expect to see a voltage drop like that with a 40A load unless the service was already loaded up near the max.

I would start measuring at the meter and see what's there and then at the meter main.

If the service size is say 200 amps and the the total load for the house is say 50-60-70 amps and the voltage drop is already down to 230 then what happen if the the load were to increase to wells over a 100 amps. A water heater, dryer, electric range or other combination of heavy loads were added.

Until I could prove otherwise I would be thinking of a loose connection and I have found several over the years.
 
If it is a pure 240V load there can be no current on the neutral.
But an asymmetric voltage drop on L1 and L2 would indicate a single bad connection or damaged wire and tell you which side it is in.

Sent from my Pixel 4a using Tapatalk
 
It’s 200 amp service. Heater is straight 240 volt. The voltage drop I read was with only the heaters running minus some small lights.
So yes when a stove kicks on and the heat turns on there going to be some large vd if I don’t find the problem lol
 
AC\DC said:
It’s 200 amp service. Heater is straight 240 volt. The voltage drop I read was with only the heaters running minus some small lights.
So yes when a stove kicks on and the heat turns on there going to be some large vd if I don’t find the problem lol
Click to expand...
You may not have a problem.
Measure the voltage at the Meterbase or wherever the POCO POD is at.
It could be as easy as measure voltage, call the POCO to install a bigger triplex
 
Hv&Lv said:
You may not have a problem.
Measure the voltage at the Meterbase or wherever the POCO POD is at.
It could be as easy as measure voltage, call the POCO to install a bigger triplex
Click to expand...
Sure it can be the triplex is to small but it could be just a bad crimp intalled either by other electrician or the utility company themselves. They used to use hand crimpers and not all splices were that great.

Around here I would get them to bring the "Beast" and put their own load on the line to verrify their equipment is bad.
 
211025-2356 EDT

AC\DC:

I suspect the power company wires are sufficiently large to handle you load current. If they don't overheat, then they are basically safe.

.
 
AC\DC said:
I had the FLIR for my iPhone thing was junk went through three. Since that incident I have been reluctant to try another one, I know I need one
Click to expand...
Dream big! :p

FLIR E4 Compact Thermal Imaging Camera

61dON+UIFqL._AC_SL400_.jpg
 
Made it out today and gave it another lock.
I messed up on describing the poco meter location.
There meter is 250’ away from the house. There pole mounted transformer is 15’ feet from the meter. Did not see originally tucked in trees.
Wire feeding there transformer is 1/0

On the house is an old meter location that has stabs in jaws and then feeds the house.

my voltage measurement were from the panel 250’ away from meter.

poco came out and did not find anything g on there end. Though the line man said why don’t you install 240 volt heater with neutral to balance the loads so I don’t t know if he new to much.

I checked voltage today and difference was not as bad will be checking the old meter location connection.
Figured I update with the correct information

I still have some high resistant connection somewhere. The VD calculator I used said at 240 volt with 40 amp load at 250’ with 4/0 alum, VD should be about 1 volt.
 
AC\DC said:
Made it out today and gave it another lock.
I messed up on describing the poco meter location.
There meter is 250’ away from the house. There pole mounted transformer is 15’ feet from the meter. Did not see originally tucked in trees.
Wire feeding there transformer is 1/0

On the house is an old meter location that has stabs in jaws and then feeds the house.

my voltage measurement were from the panel 250’ away from meter.

poco came out and did not find anything g on there end. Though the line man said why don’t you install 240 volt heater with neutral to balance the loads so I don’t t know if he new to much.

I checked voltage today and difference was not as bad will be checking the old meter location connection.
Figured I update with the correct information

I still have some high resistant connection somewhere. The VD calculator I used said at 240 volt with 40 amp load at 250’ with 4/0 alum, VD should be about 1 volt.
Click to expand...
Do you have 4/0?
 
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