Wondering how to figure out what the ARC Flash PPE requirement is for doing online motor testing with the Baker Instruments (now SKF) Explorer Dynamic Motor Tester. I test mostly 4160V motors in the MCC. I have to open the control panel door of the cubicle to get to the back of the Multilin Relay. I have to connect my voltage leads and portable CT clamps to the back of the Multilin. Keep in mind this is all control voltage I'm dealing with.

I am protected (in my opinion) by the "Second" inner door of the cubicle that seperates the control voltage portion from the 4160V portion, so I'm only exposed to the low voltage terminal strips and such. I'm looking at NFPA-70E, Table 130.(C)(15)(a). Some scenerios have a Hazard/Risk Category "0" and some a "1" or "2"...

Just wondering if anyone else deals with this...

There are basically 3 sources in the control cabinet. First there is usually control power which is usually 120 V AC. It may be driven by a CPT in the medium voltage section or it may be common to several buckets. Second you have CT leads which are limited in the amount of power by the CT's but the voltage can be arbitrarily high during a fault. Finally there is some external signalling and possibly PT's, ignoring very low voltages (communications cabling).

For 120 V I am not aware of any published data showing arcs exceeding 1.2 cal/cm^2 but there are a few OSHA investigations where hospitalization occurred on the hands due to close proximity to an arc. 208 V 3 phase has more research and sustainable arcs do exist, and OSHA investigated a single case in 2009 involving a fatality with a 240/120 construction panel. Right now IEEE 1584 gives guidance of less than 1.2 cal if fed by a single transformer rated 208 V or less, and 125 kVA or less. NESC gives guidance of 4 cal for everything under 300 Volts because this is the lowest rating accepted in the utility industry. So the short story is generally everything is under 1.2 cal but pay attention to transformer sizes. If they are large, I would roll up to the NESC recommendation of 4 cal.

Second consideration is shock. Multilins don't have a lot of "finger safe" guarding. Thats not to say though when the distance in the table is "avoid contact" that the instrument handles don't count (see IEEE 516 since 70E gets their info from that source and is utterly unclear on specific shock protection work methods). With the CT's the rubber gloves should definitely come out because if a CT lead breaks you have a very high voltage fault to contend with.

Further to the posibility of open circuiting the CT, the high voltage produced also exists at the CT secondary terminals which is in the MV compartment. There is a chance of the CT failing or flashing over which could escalate to a MV flashover.

I have witnessed an open circuited CT at 4160V. The growling noise is quite memorable. In one case I was removing a draw-out style relay and the CT shorting links didn't work right. I received a shock and a small blister on my hand where I was holding the relay.

What are you talking about???? This post doesn't make any sense!!!


FYI: Referenced post was deleted as being irrelevant and possible spam. wbd