I have an installation that has a bull rail with 12 headbolt receptacles at a trucking company. Individual circuits out to each receptacle from a panelboard that is located adjacent to the bullrail. The GFI are tripping at the receptacle, but only when it's below -10 degrees (F). Anything warmer than that and they all work fine. We inspected the installation and everything looks fine, properly grounded etc. The only "quirk" in the installation is they used a shared neutral but they pigtailed it properly and we checked with the receptacle manufacturer and they sent us a diagram that indicated the installation was proper. My first inclination is we are overloading the circuits (i.e the colder it gets the more power the headbolts are pulling), but why wouldn't the circuit breakers at the panelboard be tripping then, instead of the GFI's. Anybody ever come up against something like this before?
GFI's at Headbolt Tripping
- Thread starter tommya
- Start date
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Cow
Senior Member
- Location
- Eastern Oregon
- Occupation
- Electrician
What are headbolts? Is that another name for block heaters?
I've never heard of your problem, when you contacted the manufacturer what did they say about the temperature? Have you tried another brand GFCI? Have you megged the load that is being plugged into them when it's at -10 degrees?
I've never heard of your problem, when you contacted the manufacturer what did they say about the temperature? Have you tried another brand GFCI? Have you megged the load that is being plugged into them when it's at -10 degrees?
Yes sorry we call block heaters, headbolt heaters here. No we have not been able to megger because we are past our cold season now and it has just recently been brought to our attention. We checked the other day when it was 39 degree F and we got 12 amps at one and 15 at the other (the only two trucks around). Maybe a better questions is if anyone has had issues with GFI tripping on overload instead of the breaker. It would just seem to me that the breaker should trip and not the GFI. We have two different types of GFI receptacles out there Leviton and Cooper, they both act the same.
cadpoint
Senior Member
- Location
- Durham, NC
Best Guess
Best Guess
Are the GFCI in cast FX box ? If they are I'd seal the box, If there is no cast metal box's, I'd put them in and seal it.
In all cases I wouldn't install directly below the drop or another device, but loop to the side so that there is a collection point, and still seal any opening accordingly.
The humidity it being drawn to the electronic circuits of the working GFCI.
PS: One should have noticed drops or staining in the existing box, its a condensation problem
Best Guess
Are the GFCI in cast FX box ? If they are I'd seal the box, If there is no cast metal box's, I'd put them in and seal it.
In all cases I wouldn't install directly below the drop or another device, but loop to the side so that there is a collection point, and still seal any opening accordingly.
The humidity it being drawn to the electronic circuits of the working GFCI.
PS: One should have noticed drops or staining in the existing box, its a condensation problem
Last edited:
- Location
- Illinois
- Occupation
- retired electrician
GFCI receptacles have no way to detect an overload. They only trip when there is leakage current.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
100326-0831 EST
The National Semiconductor GFCI chip is used in the Leviton and has an operating temperature range of -40 to +70 deg C. The Cooper probably uses the same chip. These would come from different manufacturing batches. Thus, unlikely this basic element would be the problem.
There are other components in the GFCI that might have temperature problems, but unlikely at the low temperature end vs high temperature. Generally leakage resistance goes down as temperature goes up, and this is the wrong direction to cause problems.
The internal test resistor in GFCIs is 15,000 ohms. This produces 8 MA at 120 V. If the sensitivity of the GFCI increased as temperature decreased, then you would need to be experimenting with test leakage resistance above 15,000 ohms. 5 MA at 120 is 24,000 ohms (use a 22 k or 27 k), 2.5 MA at 120 is 48,000 (use a 47 k), 100k would produce 1.2 MA. 1/2 W resistors would be OK for momentary use.
It might be worth while to take several of the GFCIs that had caused problems and put them in a freezer and run load and leakage current tests. It is true that load current should have virtually no effect on the GFCI. But under sever temperature conditions one can not rule out some strange effect. This is why my neighbor, before retirement chief engineer of Ford light truck chassis, insisted on real world field tests under actual environment conditions. He would not depend on on laboratory tests alone. This was especially true on seals.
You have a different latching mechanism in the Leviton and Cooper GFCIs, and therefore that area is an unlikely cause.
When it gets cold again and the problem reoccurs, then take a hair dryer and heat the GFCI, and see if this corrects the problem. If it does, then investigation of GFCI problems should be considered. If not, then somewhere after the GFCI is the problem.
I like the ideas of moisture, and or problems in the load presented in the previous posts.
If you have available CO2. a suitable valve, a small orifice, and a siphon tank or turn a standard tank upside-down, then you can generate a very low temperature for testing the the GFCIs in place.
Easier maybe, but harder to control temperature, is packing dry ice around the box. You do not want to cool the GFCI too much.
With liquid CO2 you can get down to -73 deg C.
http://en.wikipedia.org/wiki/Dry_ice
http://www.associatedenvironmental-bma.com/models/bd.asp
http://www.electrotechsystems.com/getManual.asp?DocID=92
.
The National Semiconductor GFCI chip is used in the Leviton and has an operating temperature range of -40 to +70 deg C. The Cooper probably uses the same chip. These would come from different manufacturing batches. Thus, unlikely this basic element would be the problem.
There are other components in the GFCI that might have temperature problems, but unlikely at the low temperature end vs high temperature. Generally leakage resistance goes down as temperature goes up, and this is the wrong direction to cause problems.
The internal test resistor in GFCIs is 15,000 ohms. This produces 8 MA at 120 V. If the sensitivity of the GFCI increased as temperature decreased, then you would need to be experimenting with test leakage resistance above 15,000 ohms. 5 MA at 120 is 24,000 ohms (use a 22 k or 27 k), 2.5 MA at 120 is 48,000 (use a 47 k), 100k would produce 1.2 MA. 1/2 W resistors would be OK for momentary use.
It might be worth while to take several of the GFCIs that had caused problems and put them in a freezer and run load and leakage current tests. It is true that load current should have virtually no effect on the GFCI. But under sever temperature conditions one can not rule out some strange effect. This is why my neighbor, before retirement chief engineer of Ford light truck chassis, insisted on real world field tests under actual environment conditions. He would not depend on on laboratory tests alone. This was especially true on seals.
You have a different latching mechanism in the Leviton and Cooper GFCIs, and therefore that area is an unlikely cause.
When it gets cold again and the problem reoccurs, then take a hair dryer and heat the GFCI, and see if this corrects the problem. If it does, then investigation of GFCI problems should be considered. If not, then somewhere after the GFCI is the problem.
I like the ideas of moisture, and or problems in the load presented in the previous posts.
If you have available CO2. a suitable valve, a small orifice, and a siphon tank or turn a standard tank upside-down, then you can generate a very low temperature for testing the the GFCIs in place.
Easier maybe, but harder to control temperature, is packing dry ice around the box. You do not want to cool the GFCI too much.
With liquid CO2 you can get down to -73 deg C.
http://en.wikipedia.org/wiki/Dry_ice
http://www.associatedenvironmental-bma.com/models/bd.asp
http://www.electrotechsystems.com/getManual.asp?DocID=92
.
It's all the GFCI's, there doesn't seem to be any one that does it more or less. Nor is there a particular vehicle that does it more or less. More information, we are in Alaska, but we are a coastal community and have the same exact set-up (Block heater rail) in an interior community (i.e. hundreds of miles from shore) at another facility that gets even colder but doesn't have any issues at colder temperatures, with like i said a similiar set-up. So given the previous post i'm thinking the condensation/humidity at colder temperatures is the issue. Thanks for all the responses, we are going to get the install sealed up and hopefully that solves it. But we won't know until next sept/oct or so now!!
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
100327-0804 EST
tommya:
Very important information in your last post. GFCIs in a location far from the coast have no problem in comparable temperature conditions.
I can guess that your coastal atmosphere has a moderate amount of salt in the air. This can deposit on surfaces. With moisture added to this surface you get a conductive layer that has a resistance low enough to trip the GFCI.
If I run our ultrasonic humidifier with our tap water everything in the room is coated with a white dust from the salt deposits in our water. These are mostly calcium. Run distilled water and there is no residue.
If I run conductivity tests with a probe for this purpose and measure distilled water from Kroger or Absopure I gets results consistent with published data on distilled water conductivity. Basically distilled water is very non-conductive, but when exposed to air the CO2 in the air is dissolved in the water making the water very slightly conductive.
http://www.lenntech.com/applications/ultrapure/conductivity/water-conductivity.htm
If I test various manufacturers of filtered water I get conductivity that is considerably greater than distilled water. And our tap water is lower yet.
If I boil our tap water on the stove for several days and add additional water as needed, then I can increase the salt concentration further.
You might expect top surface snow to be nearly pure water when melted. Not so. There is contamination in the air that is collected by the snow as it falls. Thus, melted snow in our area has a moderate amount of conductivity as compared to distilled water. Therefore as a source of water for my humidifier I now stay with bottled water that is steam distilled. Some vendors claim their reverse osmosis filtered water is comparable to distilled water. Those that I have checked are not.
This above is background for your problem.
At this point I am guessing that evaporated water from the ocean may be quite pure, but there may be substantial mechanically created water drops with salt that are transferred into the air. This in turn may mean that the air may deposit salts on surfaces. The conductivity of the salt without moisture may be low, but when moisture (water) is added ionization takes place in this surface coating providing some degree of conductivity. So under low temperature condensing conditions some surfaces in the GFCI become sufficiently conductive to trip the device.
I suggest that you try some of your own experiments and/or send samples of GFCIs that have tripped to the manufacture of the GFCI with an accurate description of your problems and the difference between inland and your coastal location.
A visual inspection might indicated if there is some surface deposit. Also you could power a GFCI and expose it to steam from a teakettle and see if that would trip it. These would be the simplest experiments.
.
tommya:
Very important information in your last post. GFCIs in a location far from the coast have no problem in comparable temperature conditions.
I can guess that your coastal atmosphere has a moderate amount of salt in the air. This can deposit on surfaces. With moisture added to this surface you get a conductive layer that has a resistance low enough to trip the GFCI.
If I run our ultrasonic humidifier with our tap water everything in the room is coated with a white dust from the salt deposits in our water. These are mostly calcium. Run distilled water and there is no residue.
If I run conductivity tests with a probe for this purpose and measure distilled water from Kroger or Absopure I gets results consistent with published data on distilled water conductivity. Basically distilled water is very non-conductive, but when exposed to air the CO2 in the air is dissolved in the water making the water very slightly conductive.
http://www.lenntech.com/applications/ultrapure/conductivity/water-conductivity.htm
If I test various manufacturers of filtered water I get conductivity that is considerably greater than distilled water. And our tap water is lower yet.
If I boil our tap water on the stove for several days and add additional water as needed, then I can increase the salt concentration further.
You might expect top surface snow to be nearly pure water when melted. Not so. There is contamination in the air that is collected by the snow as it falls. Thus, melted snow in our area has a moderate amount of conductivity as compared to distilled water. Therefore as a source of water for my humidifier I now stay with bottled water that is steam distilled. Some vendors claim their reverse osmosis filtered water is comparable to distilled water. Those that I have checked are not.
This above is background for your problem.
At this point I am guessing that evaporated water from the ocean may be quite pure, but there may be substantial mechanically created water drops with salt that are transferred into the air. This in turn may mean that the air may deposit salts on surfaces. The conductivity of the salt without moisture may be low, but when moisture (water) is added ionization takes place in this surface coating providing some degree of conductivity. So under low temperature condensing conditions some surfaces in the GFCI become sufficiently conductive to trip the device.
I suggest that you try some of your own experiments and/or send samples of GFCIs that have tripped to the manufacture of the GFCI with an accurate description of your problems and the difference between inland and your coastal location.
A visual inspection might indicated if there is some surface deposit. Also you could power a GFCI and expose it to steam from a teakettle and see if that would trip it. These would be the simplest experiments.
.
kwired
Electron manager
- Location
- NE Nebraska
How about placing a resistor in the outlet box to reduce condensation possibilities and to increase temperature inside the enclosure? Only 5 watts or even less may make a pretty big difference in a FS box. Try it on just a couple and see if it works.
ptonsparky
Tom
- Occupation
- EC - retired
I am guessing that you are sure you do not have a problem with the heaters or cords. Perhaps the GFCI is doing its job?
Cow
Senior Member
- Location
- Eastern Oregon
- Occupation
- Electrician
I agree.
I'll say it again, you should meg everything first, block heaters go bad, cords wear out. It only takes a few minutes to do....
cadpoint
Senior Member
- Location
- Durham, NC
slick 50
Senior Member
- Location
- 6 super bowl ring city
How about trying to remove the GFI receptacle for at least one circuit and installing a GFI breaker. If the problem has anything to do with the GFI device getting too cold, then the problem should go away. If it is truly an issue with the current leakage of the block heaters, then the GFI breaker should trip too. This may help break down the troubleshooting steps and pin point what the issue is.
kwired
Electron manager
- Location
- NE Nebraska
210.8(B)(4) requires all 15 and 20 amp 125 volt receptacles outdoors to have GFCI protection with very few exceptions.
They do not have to be a GFCI type receptacle however, a GFCI circuit breaker could supply it, or an upstream GFCI receptacle.
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