Sizing and protection of tap wires

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ToddB

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A guy at the facility where I'm working wants to install finger-safe test jacks in a box nippled to the side of a disconnect switch so that the electricians can perform live-dead-live tests when locking out the disconnect. The disconnect feeds span wires for two overhead bridge cranes and I believe the wiring is 4 AWG. The test jacks would be tapped from the downstream side of the disconnect and I believe that he wants to use 10 AWG or smaller from the tap point to the test jacks. The taps to the test jacks would be less than 2 feet long and would be un-fused. Does the NEC allow taps to test jacks, using wire smaller than the protection of the main feeder, without over-current or short circuit protection of some sort for the smaller wire?

Thanks all.
 
If the NEC allows it, do you really want to do that way?
Touch safe is great for voltage, but if somebody make a mistake and ends up connecting a short circuit to the jacks, I would rather have either a current limiting resistor or a fuse in the circuit for their protection. The wires inside the box may be able to fuse and vaporize without too much harm, although that might then trigger an arc flash incident inside the box. That would not be cool.
 
I agree. I don't see harm in fusing the taps, but I don't think that's the way they're heading. I just can't find anything in the NEC specifically addressing this sort of situation.

Thanks for the response.

GoldDigger said:
If the NEC allows it, do you really want to do that way?
Touch safe is great for voltage, but if somebody make a mistake and ends up connecting a short circuit to the jacks, I would rather have either a current limiting resistor or a fuse in the circuit for their protection. The wires inside the box may be able to fuse and vaporize without too much harm, although that might then trigger an arc flash incident inside the box. That would not be cool.
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ToddB said:
I agree. I don't see harm in fusing the taps, but I don't think that's the way they're heading. I just can't find anything in the NEC specifically addressing this sort of situation.

Thanks for the response.
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I can see the argument that the fuse is a point of failure in the dead test, on the rare chance that the fuse opens in the middle of the test.

Tapatalk!
 
A philosophic question.

A philosophic question.

To fuse or not to fuse, that is the question?

(1) If we fuse these "potential" wires then we run the risk of a fuse opening and we believing that there is no voltage on the circuit when there is.

(2) If we don't fuse these wires then we run the risk that the wire(s) will fail or overheat if they are faulted in some manner. (Or that the test leads being used with them fault and cause a problem.)

In case (1) is there a separate measurement made by some other means before we put people or property at risk? If not, then we probably should not fuse them.

In case (2) what is the realistic level of hazard of the wires being faulted?

For another or related approach I've come across a variety of devices for showing voltage status called SAFESIDE?

I have no relationship with them but think their ideas may be useful to the OP.

http://graceport.com/cms/wp-content/uploads/2013/10/Permanent_Electrical_Safety_Devices_PESDs.pdf

MODERATORS: Please wack this if it trespasses into advertising.
 
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fmtjfw said:
To fuse or not to fuse, that is the question?

(1) If we fuse these "potential" wires then we run the risk of a fuse opening and we believing that there is no voltage on the circuit when there is.

(2) If we don't fuse these wires then we run the risk that the wire(s) will fail or overheat if they are faulted in some manner. (Or that the test leads being used with them fault and cause a problem.)

In case (1) is there a separate measurement made by some other means before we put people or property at risk? If not, then we probably should not fuse them.

In case (2) what is the realistic level of hazard of the wires being faulted?

For another or related approach I've come across a variety of devices for showing voltage status called SAFESIDE?

I have no relationship with them but think their ideas may be useful to the OP.

http://graceport.com/cms/wp-content/uploads/2013/10/Permanent_Electrical_Safety_Devices_PESDs.pdfhttp://

MODERATORS: Please wack this if it trespasses into advertising.
Click to expand...

Do you have a link that works? I get a 404 error for that link... :)
 
From one of the products on that link. I didn't check all of them, but I think they are all the same.
Voltage is the common denominator in an electrical accident or an arc flash; no voltage means no accident, no arc flash. While performing electrical LOTO with a thru-door voltage detector installed, the electrician can pre-check the internal voltage state without opening the enclosure. Next, the
electrician should replicate a zero voltage reading with his voltmeter as per NFPA 70e 120.1(5). This low-cost, redundant voltage-verification task reduces arc flash risk and increases electrical safety for workers.
Click to expand...
As far as I know the only OSHA permitted method of proving there is no voltage is by using a meter. That being said, this device gives you good assurance that there is no voltage before you use your meter to prove that there is no voltage and that makes the operation safer. Note, that until you prove that there is no voltage with the meter, you will have use voltage and arc flash PPE suitable for the system.
 
don_resqcapt19 said:
...As far as I know the only OSHA permitted method of proving there is no voltage is by using a meter. ...
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OSHA uses the term....

1910.333(b)(2)(iv)(B)

A qualified person shall use test equipment to test the circuit elements and electrical parts of equipment to which employees will be exposed and shall verify that the circuit elements and equipment parts are deenergized. The test shall also determine if any energized condition exists as a result of inadvertently induced voltage or unrelated voltage backfeed even though specific parts of the circuit have been deenergized and presumed to be safe. If the circuit to be tested is over 600 volts, nominal, the test equipment shall be checked for proper operation immediately after this test.
Click to expand...

Does OSHA have specific requirements on what qualifies as test equipment?
 
Smart $ said:
OSHA uses the term....



Does OSHA have specific requirements on what qualifies as test equipment?
Click to expand...

Well, for one thing, if used on over 600V, the requirement to check the test equipment after each test could be hard to do with any of the permanently attached products. :)
 
GoldDigger said:
Well, for one thing, if used on over 600V, the requirement to check the test equipment after each test could be hard to do with any of the permanently attached products. :)
Click to expand...
I didn't look at the product(s) mentioned earlier... but let's say you had a permanently installed voltmeter with a switch that connected it to either line or load. It indicates load side as live, then indicates deenergized after you open the disconnect. Switch meter to line and meter indicates live. Switch back to load and it still indicates dead.

Is this any different than doing a live-dead-live test with portable test equipment?
 
GoldDigger said:
No difference if you trust the switch. But you cannot verify it directly.
Click to expand...
How is trusting the switch any different than trusting placement your meter leads. Haven't you ever placed meter leads and didn't get a good reading?

Not sure I understand what you're saying about not being able to verify it directly.
 
From a Fluke document
Low-voltage proximity or non-contact voltage testers. These little tools are good for a first test, but should always be followed up with a direct-contact meter. ... The real issue is that proximity testers may indicate voltage, or they may not, depending on specific circumstances. For absence of voltage testing, a different, completely reliable test method is required.
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Yes, I know that this document is not from OSHA and stops short of actually saying that you can't use a non-contact tester to prove the voltage is off.
 
fmtjfw said:
To fuse or not to fuse, that is the question?

(1) If we fuse these "potential" wires then we run the risk of a fuse opening and we believing that there is no voltage on the circuit when there is.

(2) If we don't fuse these wires then we run the risk that the wire(s) will fail or overheat if they are faulted in some manner. (Or that the test leads being used with them fault and cause a problem.)

In case (1) is there a separate measurement made by some other means before we put people or property at risk? If not, then we probably should not fuse them.

In case (2) what is the realistic level of hazard of the wires being faulted?

For another or related approach I've come across a variety of devices for showing voltage status called SAFESIDE?

I have no relationship with them but think their ideas may be useful to the OP.

http://graceport.com/cms/wp-content/uploads/2013/10/Permanent_Electrical_Safety_Devices_PESDs.pdf

MODERATORS: Please wack this if it trespasses into advertising.
Click to expand...

Sorry I sometimes get a pasting error in which the default http:// gets appended rather than replaced.
 
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