metering devices

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Hey All,

New to this forum, can't seem to find a suitable answer to this in the code book.

First a little bit about the layout;

We have standby generator that we use when we lose utility power, it is an older setup, and does not have an automatic transfer switch. We only use the generator if the power company tells us the outage will last more than a couple hours, and that is just to run our refrigeration, not the whole facility.

There is a 1200A disconnect from our main switch-gear that feeds the "utility" side of our transfer switch which we use to isolate before changing the transfer switch between utility or generator power.

I would like to install analog volt meters (power monitoring, not service meters) on the panel door of this 1200A disconnect. Three 0-600V meters, monitoring leg to leg voltage (A-B B-C C-A) on the line side of this switch.

the purpose of the meters is two-fold, first under normal conditions this will give us a place to take a quick look at incoming voltage, or if something seems amiss a place to quickly check for a brown-out/black-out condition of a leg.
secondly, when we are running on generator power, it would allow us to monitor whats going on with the utility side.

Now, for the actual question;

How does the tap rule apply to this (240.21/B)?
Or does it?
Or would a monitoring device fall under some other code?

I have seen in other panels, where a manufacturer has some monitoring device (like a ground fault or under-voltage monitor), that is fed with 14 gauge wires tagged right onto a 4000A buss.

Can I just tag these meters onto the line side lugs?
Should I provide a breaker between the line and meters (more for the convenience of disconnecting the meters for replacement)?

Anyone out there had experience doing something like this?

Regards,
JohnR
 
John, the way this is typically done is to use a transformer to step the voltage down and limit fault current to the voltage meter. This "potential transformer" would have fuses.

On the typical 480 volt service the transformer would step it down to 120 volt. The panel meter would be scaled to display 120 volts as 480 volts. You would have a rotary switch that would allow you to measure each phase to ground as well as phase to phase voltages. This is "old school" and today most boards have a digital one that will display volts, current, distortion, etc.

Another way to go would be to add a surge protector. They don't display voltage but have LEDs for each phase.

The Cadillac solution is to get a real ATS. It will display voltage and current from both sources.


P.S. I would contact the manufacturer of the switch gear for a turn key meter solution that is UL listed.
 
John, If you have a fused switch tap on your service board, you may consider looking at something like this. ICM 450

It's not analog, but has the functions your looking for in an economical package, could be useful on the equipment side too.
MTW
 
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