Power tools extension cord voltage drop - more than should be? How much is too much

Todd0x1

Senior Member
Location
CA
I'm under the impression that OSHA requires the grounded conductor to be opened. Portable GFCI have this capability. I believe I read it from ECM or something similar. I'll look for it

OSHA requires both open neutral and overvoltage protection in portable GFCIs. This is why spider boxes have the separate GFCI modules and not GFI breakers or receptacles. The open neutral protection prevents the GFCI from having voltage on its load side if the supply neutral is lost (which would prevent a normal GFCI from functioning) or is at a high voltage.
 
I've seen a lot of spider boxes with GFCI breakers or receptacles; the modules are usually $$$$$$ and a pain to replace.

(Like the NEC, when someone says "OSHA says" there should have a citation so the rest of us can look it up.)
 

Todd0x1

Senior Member
Location
CA
That link says nothing about requiring separate GFCI modules.

Neither does UL1640, but the separate modules are the only way to achieve the required open neutral or overvoltage protection. There is no GFCI breaker or GFCI receptacle that can provide the required protection.
 
The OSHA page specifically mentions receptacle GFCIs--
For construction applications, there are several types of GFCIs available, with some variations:
Receptacle Type:
It does mention that no-voltage release in portable and cord-connected units, but not that those functions are required in general. That page does not mention over-voltage or open-neutral at all. Please find me the page that does.

However....
tells us that "For purposes of this response, "open-neutral protection" refers to the ability of a GFCI to trip even if there is an open-neutral condition." and "A GFCI that does not have "open-neutral protection" is permitted to be used under the OSHA standard if it is approved by a qualified testing laboratory in accordance with §1926.449(a)." None of that tells us that receptacle GFCIs are not allowed (nor GFCI breakers which could be considered separate modules).

I'm also having trouble understanding how a GFCI that is watching the current balance between the hot and grounded conductors would not operate if the grounded one was open (current goes out one lead & doesn't come back the other=trip). Are there 120v GFCIs that don't watch the current balance?
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
The OSHA page specifically mentions receptacle GFCIs--

It does mention that no-voltage release in portable and cord-connected units, but not that those functions are required in general. That page does not mention over-voltage or open-neutral at all. Please find me the page that does.

However....
tells us that "For purposes of this response, "open-neutral protection" refers to the ability of a GFCI to trip even if there is an open-neutral condition." and "A GFCI that does not have "open-neutral protection" is permitted to be used under the OSHA standard if it is approved by a qualified testing laboratory in accordance with §1926.449(a)." None of that tells us that receptacle GFCIs are not allowed (nor GFCI breakers which could be considered separate modules).

I'm also having trouble understanding how a GFCI that is watching the current balance between the hot and grounded conductors would not operate if the grounded one was open (current goes out one lead & doesn't come back the other=trip). Are there 120v GFCIs that don't watch the current balance?
I’m sort of lost too on this. I thought GFCIs worked with super sensitive differential protection. Open neutral no current flows…
why would it open?
 

Todd0x1

Senior Member
Location
CA
The OSHA page specifically mentions receptacle GFCIs--

It does mention that no-voltage release in portable and cord-connected units, but not that those functions are required in general. That page does not mention over-voltage or open-neutral at all. Please find me the page that does.

However....
tells us that "For purposes of this response, "open-neutral protection" refers to the ability of a GFCI to trip even if there is an open-neutral condition." and "A GFCI that does not have "open-neutral protection" is permitted to be used under the OSHA standard if it is approved by a qualified testing laboratory in accordance with §1926.449(a)." None of that tells us that receptacle GFCIs are not allowed (nor GFCI breakers which could be considered separate modules).

I'm also having trouble understanding how a GFCI that is watching the current balance between the hot and grounded conductors would not operate if the grounded one was open (current goes out one lead & doesn't come back the other=trip). Are there 120v GFCIs that don't watch the current balance?

On standard GFCIs the trip mechanism is latching and requires incoming power to operate and trip. An energized GFCI receptacle (or breaker) with the incoming neutral lost will continue to pass voltage on the hot side and will not trip on a downstream ground fault.

The GFCI modules used in the Spider Boxes do not have a latching mechanism. Upon receiving power they run a check then close a relay that energizes the output terminals. Loss of the incoming neutral causes that relay to drop out.

Ul1640 Part 4 (Construction site equipment for temporary installations in accordance with NEC 590) Section 57 governs the GFCI requirements. In summary, the equipment (the spider box) has to continue to provide class A GFCI protection to its 120v output circuits if either the grounded conductor (neutral) is open OR if any of the supply conductors is transposed with the grounded conductor -so if a cable is miswired or damaged such that the neutral input to the spider box is hot the GFCI modules won't close.
 

GeorgeB

ElectroHydraulics engineer (retired)
Location
Greenville SC
Occupation
Retired
I thought GFCIs worked with super sensitive differential protection. Open neutral no current flows… why would it open?
Current flow from "hot" through a body to that pesky dirt. Differential SHOULD, imho, open the hot even so.
 
Now we're getting somewhere- open neutrals on the LINE side of the GFCI (first time that's been mentioned and it's quite important to the discussion). We also still run into the letter of July 7, 2003, the OSHA page "Ground-Fault Circuit Interrupters (GFCI)" which identifies GFCI receptacles as possibly acceptable, and a few others. Like a lot of points, OSHAs interpretations can be contradictory.

Open neutral no current flows… why would it open?
From hot to EGC or any leakage that takes current back to the source bypassing the sensing element.

At this point, Todd has the advantage of me since I don't have a copy of UL1640 and can't find a free version, and recently purchased spider boxes have GFCI receptacles which suggests that modules aren't a hard requirement. And I can't call any manufactures over the weekend.

There's no reason to continue the discussion without having the UL requirements and a better survey of OSHA's interpretations.
 

Todd0x1

Senior Member
Location
CA
Now we're getting somewhere- open neutrals on the LINE side of the GFCI (first time that's been mentioned and it's quite important to the discussion). We also still run into the letter of July 7, 2003, the OSHA page "Ground-Fault Circuit Interrupters (GFCI)" which identifies GFCI receptacles as possibly acceptable, and a few others. Like a lot of points, OSHAs interpretations can be contradictory.


From hot to EGC or any leakage that takes current back to the source bypassing the sensing element.

At this point, Todd has the advantage of me since I don't have a copy of UL1640 and can't find a free version, and recently purchased spider boxes have GFCI receptacles which suggests that modules aren't a hard requirement. And I can't call any manufactures over the weekend.

There's no reason to continue the discussion without having the UL requirements and a better survey of OSHA's interpretations.

What are the recently purchased spider boxes you have? I know trystar makes them with just gfci receptacles for the event industry, which would be ok just cant use them on a construction site.
 
Ah, another data point! Events vs construction!

Trystar (and others) products used for event power, although pretty much every spider box I've had from Sunbelt, TempPower, the local Cat rentals place, etc, in the last 10+ years has had either GFCI recep's or breakers; while it's possible, it's also unlikely that they keep two separate sets for different users.
 
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