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 Post subject: PPE rated for high voltage contact?
PostPosted: Thu Jan 19, 2012 12:37 am 
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Is there any PPE rated for direct HV contact besides boots+gloves?

I was interested in picking up something that was rated for withstanding both 25 cal arcflash and class 3 dielectric.

Doing work with large HV capacitor banks.

Overkill? Probably. But I'm still interested.

Edit: to clarify, I mean as in head to toe PPE, obviously not just the boots/gloves rated for HV


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PostPosted: Thu Jan 19, 2012 4:59 am 
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1.21gigawatts wrote:
Is there any PPE rated for direct HV contact besides boots+gloves?

I was interested in picking up something that was rated for withstanding both 25 cal arcflash and class 3 dielectric.

Doing work with large HV capacitor banks.

Overkill? Probably. But I'm still interested.

Edit: to clarify, I mean as in head to toe PPE, obviously not just the boots/gloves rated for HV


1. Any time someone throws around the term "high voltage", it always begs clarification, because the threshold voltage for this changes depending on the end user. The gloves that are to be worn should be rated for the nominal voltage of the system by 70E standards. In cases where the TOV is a major concern, you may want to bump this up following IEEE 516 (the source for shock hazard requirements), or NESC (if "high voltage" is the utility context). I'm sort of assuming the context is power factor correction capacitors or drives for 480-600 V MCC's and probably even medium voltage (around 1-2 kV up to around 25-35 kV depending on jurisdiction) is what you mean by "HV". If you are referring to 69kV ("high voltage" in utility terms) then my response changes somewhat because you are well outside the intended rule set for 70E where NESC would be the applicable consensus safety standard. Still, I have referred you somewhat to NESC (and IEEE 516) because I find that outside of the world of <=600V AC, the NESC has better guidelines for work rules.

2. The most important rule with working on capacitors is that you treat them as live until you've fully discharged them, even if they are disconnected from any source of power. If you are planning on working on them while de-energized, then you've got to remove any potential stored charge. Generally this is either so slow or fraught with so many unknowns that it is not considered good practice. Even just a capacitor with nothing connected to it has a series resistance but discharging via this can take a LONG time. Usual practice is to use a switch or a temporary ground equipped with a known fairly low resistor to control the discharge rate and get the job done in a reasonable amount of time (seconds vs. minutes or hours). Then you apply temporary or equipment-mounted grounds and LEAVE THEM THERE for the duration of the work. Normally discharging is a non-event. Once in a while it can get exciting, which is something you normally want to avoid. Although 70E is not very good as far as detailed procedures for doing this, ANSI/IEEE C2 (aka NESC) has detailed rules for glove work as well as insulated tool work, and the "mother document" for energized electrical work is IEEE 516. Any of these are good guides for detailed rules on using hot line sticks to attach temporary grounds for discharging or for work. The necessary PPE is still that required for shock and arc flash hazards since again, it is treated as energized until discharged, tested, and then grounded, or grounded then tested depending on the rule set (NFPA 70E or NESC) in use.

So when you are doing electrical LOTO if you are following NFPA 70E, those one or two line "extra steps" referring to using temporary grounds apply in this case.

3. So far the rules are for AC systems. Due to the fact that the capacitor can be used as a charge pump in DC systems, I recommend engineering a discharge mechanism right into the system in the DC case. If it's tolerable, even installing an intentional discharge resistor is often the simplest and best approach. Many drives are built purposely this way for this reason. IEEE 516 is going to be your best guide in this case. NFPA 70E has started to incorporate DC rules but it has a ways to go.

4. Usually people jump right into section 120 and 130 of NFPA 70E and ignore the front material as well as chapters 2 (important maintenance requirements) and 3 (extra safety rules for special situations). Do not overlook these.


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