Following up to this question.

The fire sprinkler rooms get their electricity from building's end-units. There're subpanels in each room. We are told that main panels in the end-units have a "master" breaker controlling the feed into subpanels.

As stated before, variations are wild: from 4 breakers (double-Main, Alarm, Light, Heater) to just 2 (Alarm, Heater).
Some breakers are "fixed" with contraptions, effectively preventing them from tripping! ??

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First question: Does this configuration make sense? I.e. if the main panel's "master" breaker is 20A and subpanel's Double-Main is 100A, what's the point of the 2nd one? Also, this allows the owner of the end-unit to shut off power to the fire sprinkler room. Switching to battery backups should be reported to monitoring company, and will result in somebody showing up to investigate, but still..

Bigger question: There are no electrical meters installed in the rooms. Components that I was able to identify:
• Fire Lite MS-4 Control Panel - 280W,
• Keltron RF774F Wireless Transceiver - 40W,
• Haut 42504 303 03 Heater - 1500W.
Just based on that (leaving out other unknown boxes), maximum total consumption is:

(280 + 40 + 1500 == 1820 W) * 24 hrs/day * 30 days/month == 1310 kWh / month

That is quite a lot. Heaters should not operate 24x7. But even 10% of that is comparable to unit's usage.

Is it possible to install meters between main panels and subpanels, to know precisely how much electricity each room used? How hard is that? Who besides electrical utility and fire monitoring company has to be involved?

Are there any alternatives?

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    "760.41 NPLFA Circuit Power Source Requirements. (A) Power Source. The power source of non–power limited fire alarm circuits shall comply with Chapters 1 through 4, and the output voltage shall be not more than 600 volts, nominal. The fire alarm circuit disconnect shall be permitted to be secured in the “on” position." – Holt
    – Mazura
    May 28, 2021 at 22:51
  • Didn't know that the breaker would still trip. Thank you!
    – Astrogator
    May 29, 2021 at 15:56

1 Answer 1


It is certainly possible to insert a meter, just by adding a meter pan and buying a meter (the utility does not need to be involved - it's not a utility meter, it's local to allow you to correctly distribute the cost unfairly applied to the end-unit owners in the present scheme.) Used "dumb" mechanical meters should be widely available since utilities replaced a lot of them with "smart" meters in recent years. Since it's multi-unit housing, a licensed electrician is required, and the fire alarm company needs to know when it's happening, but that should be about it - don't know if it needs a permit, but that's a LAHJ call in any case, so ask yours (or your electrician - NOT handyman.)

The 1500W heaters probably relate to the other question's room temperature sensors - there's your heating element to keep things from freezing. And probably most of your operating expense. Or the sensors may just be for alarm purposes, with the heaters on a normal thermostat.

The breakers will trip if they need to. The device on the handle prevents them from being manually turned off. They will trip regardless of the handle position, if they need to trip.

As noted many times in subpanel questions here, the sub-panel main is a local shutoff, and does not need to match the feed breaker supplying the sub-panel. So a 20A feed to a 100A sub-panel main is perfectly legit.

  • Thank you again for good info! What does LAHJ stand for? Heaters need a separate question, will ask in a bit. Agree that they probably are the main power consumers. Didn't know breakers trip irrelevant of the handle.
    – Astrogator
    May 29, 2021 at 16:06
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    @Astrogator: "LAHJ" is "local authority having jurisdiction". May 29, 2021 at 16:54
  • Thank you! I figured L,H and J. Surprisingly Google got me nowhere :)
    – Astrogator
    May 29, 2021 at 23:12

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