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#222081 01/09/23 12:28 PM
Joined: Apr 2002
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triple Offline OP
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I don't believe I have ever seen one of these "legally" hooked up when monitoring an entire service or electrical panel. They require not only ct's for the lines being monitored but also a physical connection to each phase. Inevitably, the "electrician" will stub the meter feeds into the main lugs of a panel or into an existing, often large, breaker already in use. The meter requires in-line fuses, and the tap rule is an option. However, the main lugs, in many cases, are unfused (I know some people don't like these wires termed this way) so a tap rule would not apply. And only certain items are allowed on the service line side of equipment. Also, lugs are rated for not only number but size of wire. Usually, the install will fail for both of these reasons. The wires would need to be spliced before entering a breaker lug too. The only correct ways to feed such a power meter appears to be providing its own breaker or creating a splice with wires to an existing breaker. However, whenever that shared breaker is turned off (perhaps to service the equipment it is feeding) power will no longer be monitored. Large MDP's may not have a practical way to add a two or three pole breaker. Some people may tap a lug to the main buses, but what manufacturer is going to give the OK to make that mod?
Any input/comments?

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Joined: Jul 2004
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I agree, if there are no manufacturer tapped holes in the bus for a feed through lug this is going to be an issue. I assume these are just "gee whiz" meters and not revenue meters. All of the other splicing things come with their own issues. Maybe an ILSCO® KUP-L-Tap® ?


Greg Fretwell
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triple Offline OP
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These are meters at individual building on a military base. Once the power enters the base from the utility, everything beyond that is owned and maintained by the base. I believe the meters are just for budgeting/monitoring. BTW, add-on surge suppressors are often improperly wired in similar ways. As often as this is done, there is no doubt that others have seen this (and perhaps done it themselves). I was hoping to here from these people.

Joined: Dec 2002
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I require the physical connection (for voltage measurements) taken from a breaker in the panel or even a subpanel. I have never seen one of these "gee whiz" devices with a service rating or even close to such. They were and still required on certain Federal Gov't jobs due to supposed energy savings that can be had from monitoring, however, though tools are installed for remote monitoring, I have yet to see one be monitored. No ones job and no time to waste on frivolities at least non-military. It is not a manufacturing plant where you can actually get hints of failing equipment. Umm, you did not hear his form me.

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When I was 'working'' E-Mon meters were installed at various sites for sub-metering tenant electrical usage.

Install for the voltage tap mostly was a 3 pole, 15/20 amp breaker with a 'lock-on'. IF the E-mon required 10 amp max, a finger safe fuse holder was installed in the panel. On occasion, IF there was any available mfg. location on the buss, lugs were installed, then a fuse block as required. All were permitted and inspected.


John
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triple Offline OP
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Related question:
I can't find any requirement in the code calling for the simultaneous disconnection of 2 or 3 fuses, on ungrounded conductors, feeding a branch circuit. There are certain instances where that is required (such as multi wire branch circuits or feeders to a building or when using circuit breakers or appliances or ...). However, take my original example of a meter. I use tapped holes in MDP busses to mount lugs and feed three, separate (individual/single-pole), in-line fuseholders. The fuse holders are the insulated types that open up and the fuse (hopefully/normally) stays in the dead half. From the fuse holders, conductors feed a meter beside the panel. The only way to disconnect the meter from power,or to change fuses, is to open each fuse holder individually. However, the fuses, exposed one at a time, are "hot" due to their being in a 2 or 3 pole circuit trying to feed the meter electronics. I would think the fuse holder should be considered a disconnect satisfying 240.40 but why am I not required to simultaneously disconnect all ungrounded conductors? There are modular and multi in-line fuse holders that can perform this function. Why are they not required. Hopefully I am missing something. Thanks

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triple

Good point that I'm going to look into over the weekend. Just FYI, the last install I did was about 20 years back.

I am not aware of a multi-pole fuse block that will 'open' all poles simultaneously. Back when, I would make it a practice (after dropping out the breaker) to open all the fuse holders.


John
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NFPA probably has a problem with fuses used on line to line loads but they are fighting 125 years of using them. I suppose the place to look would be the ROPs to see why they never tightened up these rules. Personally I would not have a problem if they simply banned fuses on L/L loads without a separate disconnect like you see in the old fused water heater disconnects.
I agree with John, if you don't understand back feeding on a L/L load, you can get lit up with an inline fuse holder. I guess that is why they make those plastic fuse pullers. I always had one in my bag. 240v at 400 hz will wake you up wink


Greg Fretwell
Joined: Dec 2002
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The submeters we use, we call out in a special made cabinet for the device containment. These have the inline fuses which have special fuse blocks that limit exposure to the live parts. The fuse pops out when you access the fuse through a door in the fuse block. These are very common for small fuses now. At the same time, with the breaker at the panel off, feeding the submeter, the fuses should be unpowered.

The only issues for power at that point in the submeter is from the coils measuring current. I cannot remember if we had in place something for that. Been too long since I looked at the diagram or been in one. I think we may have fused those lines also.

Please note that these are always remote from the panelboard or switchgear they are monitoring.

When design other equipment with fusing, we design them with shut-offs before the fuses to limit exposure to live parts. Safety switches have the barriers on the line side, and with solar because both sides may be powered, you need extra poles (special design, or smart use of existing equipment) to limit the contact.
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Shane

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Shane:

" These have the inline fuses which have special fuse blocks that limit exposure to the live parts. The fuse pops out when you access the fuse through a door in the fuse block. "

Sounds like what I referred to as "finger safe", a term I got from a friend that worked for Bussmann back then.


John

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