Question: A 4160 volt motor feeder that is racked out and locked. The feeder is amoured cable. Is it necessary to apply personal protective grounds to unwire the motor? I've heard arguements that we should ground the feeder and arguments that is not needed. Any input would be greatly appreciated.
Personal protective safety grounds
- Thread starter cornbread
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zog
Senior Member
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- Charlotte, NC
cornbread said:
Yes it is necessary, MV cable is a big long capacitor. That and it is required per OSHA 1910.269 and NFPA 70E 120.1(6).
zog
Senior Member
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- Charlotte, NC
Sure assuming the sheild has continunity and all connections are sound, after 5 TC's the cable should no longer be charged, should not, which is the point.
70E says "If there is a possiblilty of induced voltages or store electrical energy......blah blah.....apply personel protective grouds rated for the available fault current in the system (Or somehting along those lines)"
The fact the cable is armored has nothing to do with it. Sheilded yes, armored, no.
70E says "If there is a possiblilty of induced voltages or store electrical energy......blah blah.....apply personel protective grouds rated for the available fault current in the system (Or somehting along those lines)"
The fact the cable is armored has nothing to do with it. Sheilded yes, armored, no.
bhsrnd
Senior Member
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- Fort Worth, TX
Not to sound crass but if it were my life in the hands of a 4,000 volt (or 120 volt or 480 volt) guessing game which could lead to a catastrophic accident I would take all the necessary precautions to ensure I went home that night and slept in my own bed. 
Although the EE may be correct, it's easy for the person NOT doing the work to make assumptions and other statements. If he were the one servicing the MV equipment I'm sure his perspective would be different.
It's like jumping out of a plane with no parachute....that's a stunt you can only do once. Better safe than sorry!
Although the EE may be correct, it's easy for the person NOT doing the work to make assumptions and other statements. If he were the one servicing the MV equipment I'm sure his perspective would be different.
It's like jumping out of a plane with no parachute....that's a stunt you can only do once. Better safe than sorry!
mdshunk
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Heck, I'll even hang macs on the bus bars of de-energized low voltage switchgear for a "just in case" insurance policy. Seems like the thing to do for the minute or two that it takes. I can't LOTO pole-top cutouts, so hanging macs is the best thing I can do. 4160 is a no-brainer, I don't care what kind of cable you think it's fed with.
bhsrnd,
I liked your analogy about jumping out of an airplane [you can only do it once. But then I thought about it....
What if the airplane was on the ground?
mdshunk,
What kind of macs are you hanging on de-energized bus bars? Are these MacIntosh computers? or apples? or raincoats?
~Peter
I liked your analogy about jumping out of an airplane [you can only do it once. But then I thought about it....
What if the airplane was on the ground?
mdshunk,
What kind of macs are you hanging on de-energized bus bars? Are these MacIntosh computers? or apples? or raincoats?
~Peter
mdshunk
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Macs is slang for any of a variety of mechanical jumpers.peter said:
zog
Senior Member
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- Charlotte, NC
mdshunk said:Macs is slang for any of a variety of mechanical jumpers.
That is a false sense of security unless they are rated for the available fault current in the system for 15 Cycles.
mdshunk
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It's better than doing nothing.zog said:
quogueelectric
Senior Member
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- new york
Not if they are not adequate to clear the fault They make these rules for a reason not for fun.mdshunk said:
mdshunk
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What rules are those that you're referring to? I think you're jumping on the objection bandwagon without any clear reference. Fact is, what I use are adequate, but given the choice between definately getting electrocuted and possibly just having a mac blow up, what do you pick? I'd hope neither, but I'm not sure what sort of protective grounds a guy might pick that can't stand a fault for 15 cycles. Certanily not anything like the type I pictured.quogueelectric said:
http://www.bluevolt.com/CoBrandTemplate/CourseDetail.aspx?CourseID=878
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zog
Senior Member
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- Charlotte, NC
mdshunk said:
NFPA 70 Etakes from OSHA 1910.269
(4)"Protective grounding equipment."(4)(i) Protective grounding equipment shall be capable of conducting the maximum fault current that could flow at the point of grounding for the time necessary to clear the fault. This equipment shall have an ampacity greater than or equal to that of No. 2 AWG copper. Note: Guidelines for protective grounding equipment are contained in American Society for Testing and Materials Standard Specifications for Temporary Grounding Systems to be Used on De-Energized Electric Power Lines and Equipment, ASTM F855-1990.(4)(ii) Protective grounds shall have an impedance low enough to cause immediate operation of protective devices in case of accidental energizing of the lines or equipment.Now before you say, "Hey mine are >no. 2 AWG" Thats not all there is to it, the entire ground set needs to be tested and rated for the fault current in the system, including the clamp and ferrel.
Here is the ASTM if you are interested
http://www.astm.org/cgi-bin/SoftCart.exe/DATABASE.CART/WORKITEMS/WK15332.htm?E+mystore
Here is the Salisbury grounding configurator
http://www.whsalisbury.com/configurator/index.php
Here is a good OSHA interpretation on other grounding issues
http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=INTERPRETATIONS&p_id=22828
bhsrnd
Senior Member
- Location
- Fort Worth, TX
peter said:bhsrnd,
I liked your analogy about jumping out of an airplane [you can only do it once. But then I thought about it....
What if the airplane was on the ground?
I would say that brings new twist on the saying "break a leg!".
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