Relay System

**Jim Robinson** · 04-01-2023, 10:11 AM

1984 house using a relay system for light switches. The wiring is well done by someone who had some experience with this type of system.
My write up noted that the #18 wires passing through the load centers would likely not be allowed today (or possibly in 1984 but I don't go there) as they would not be rated for line voltage of 15 amps or more.
The seller claims that the wires actually carry a very low amperage of 120 volts to the switches and back to the relay, and are allowed to be passing through the panels. I may have to go back to write down some relay model information. The relays are not in the load centers, but are in a separate nicely contained junction box.

Any thoughts?

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**Jerry Peck** · 04-01-2023, 12:55 PM

Jim, that was a low voltage lighting system. There were several manufacturers of them.

Think of the #18 AWG conductors in thermostat cable - that operates on a 24v transformer in the air handler/furnace and communicates with the thermostat to turn the air conditioning and/or heat on or off.

All that does is the low voltage lighting system does is, by the switch (think manual thermostat) operates a relay at each light fixture (like the air conditioner or heater) to turn it on or off. Each light fixtures is supplied by a 120 volt system for its power, ust like the air conditioning or heating system is supplied by a 240 volt or 120 volt system for its power.

Cons are: older low voltage system and finding relays may become an issue at some point in time; not practical to add dimmers to a light; etc.

Pros were/are: you can have as many switches as you want, and in as many locations as you want, with being concerned about 3-way and 4-way switches ... at the time on construction ... not easily modified now; fewer 120 volt circuits run throughout the house, so risk of shirts or arcing is reduced, reducing risk of fires.

**Jim Robinson** · 04-01-2023, 02:58 PM

Yes, I've seen the relay system before. My question was if the # 18 low volt wires can pass through the line voltage load centers. They are just passing through uninterrupted. I've always been under the impression that T stat wire, phone, coax should not pass through the load center. I personally am not that worried about it, but if Sparkey looks at it and gives it the old "Your inspector should have..." I'd like to have it noted.

Second part is that the seller states that the #18 carries low amperage 120 to the switch and back, which I don't think is correct, but until I have the relay specs I can't verify that. Why bother with the relay if it is 120 to the switch? I'm about to head overseas for a while so this one may not be answered by me. We're both okay with where we are with the report, so it's not a big deal at this point.

**Jerry Peck** · 04-01-2023, 06:17 PM

Originally Posted by Jim Robinson

My question was if the # 18 low volt wires can pass through the line voltage load centers. They are just passing through uninterrupted.

Without looking it up, my recollection is that, in 1984, that would be questionable. However, in 1985, the AHJ may very well having been working with a much older NEC version and not the 1984 edition, which could have been 10-20 older. In 1985, a lot of places were not real keen on keeping up with advances in materials, methods, and codes ... 'it's worked well for 20 years, why change it now' was a more common attitude back then as it is now.

Second part is that the seller states that the #18 carries low amperage 120 to the switch and back, which I don't think is correct, ...

That would not have been allowed back then, and I doubt that is the actually the case. If that is the case, it was definitely not the case when it was installed, but was changed by someone wanting to change things which are not changeable with those low voltage systems, so they may have just put 120 volts on those wires and said 'it has to be that way to work'.

I'm about to head overseas for a while so this one may not be answered by me. We're both okay with where we are with the report, so it's not a big deal at this point.

I'd report what the seller stated. that a licensed electrical contractor needs to verify if such is actually the case, and if so, to make any and all corrections as necessary.

That puts the onus on the electrical contractor to: a) verify what the seller told you; b) determine what needs to be done; c) and make all corrections as necessary.

**Jim Robinson** · 04-02-2023, 06:56 AM

Sounds right. We decided to leave my report as I originally wrote it, and if the buyers want to check it out they can have someone take a look at it. The panels were pretty spot on with everything else, and the relays were nicely organized and labeled.

**Dom D'Agostino** · 04-02-2023, 05:15 PM

Whomever wired and installed that panel board took great pride in their work.

**Jerry Peck** · 04-02-2023, 07:11 PM

Originally Posted by Jerry Peck

Without looking it up, my recollection is that, in 1984, that would be questionable.

Looking back at the photos I see something that I had not noticed before, provided I am seeing it correctly now: the photo in the corner with the breakers is not a close up of the same panel with the relays in it. I.e, there are two separate panels in the photos.

The relays being in their own enclosure is not an issue, back in 1984 or even now. With the key being that the relays are indeed in their own enclosure.

I originally thought that the photo with the breakers was the same enclosure, but that does not appear to be the case as I see it now.

There are conduit fill issues, and derating issues, yes, and 'back then', few paid attention to those aspects. Even today, over the last several years, I have had discussions with electrical contractors on this site who poo-pooed these exact same issues of conduit fill and derating ... some things take a very long time to change. Just a current example of 'it's worked well for 20 years, why change it now'.

**david shapiro** · 04-05-2023, 10:52 AM

I believe the main concern regarding passing low-current, low-voltage wires through an electrical enclosure is whether their insulation is listed for 300VAC. If it is, whether or not they're carrying 120VAC, voltage rating is not an issue. Current? That would mean a screw-up. I agree that it doesn't need to be flagged as demanding investigation unless there are warning signs.

Jerry's mention of the "hell, it's been working" trope is not my main reason to generally be easy about fill. Insulated wires don't take up that much space!

Imagine blanking off all holes and then filling a cabinet with water. (Ahem: this is a cabinet containing no energized conductors or parts--gedankenexperiment) Pour the water out into a (big honking) measuring beaker. Now add all those conductors and relays that had been taking up space in the cabinet. Has the water level risen enough to show they filled 40% of the gutters? 75%? More likely 15%. And that kind of test is what the NEC requirements are talking about, formally. Which leaves 110.12. Grrr. Or just a HI saying, "Looks crowded, to my judgment" when that's the case.

**Jerry Peck** · 04-05-2023, 02:17 PM

Originally Posted by Jerry Peck

There are conduit fill issues, and derating issues,

Originally Posted by david shapiro

... is not my main reason to generally be easy about fill. Insulated wires don't take up that much space!

Imagine blanking off all holes and then filling a cabinet with water. (Ahem: ...

Ahem ... did you notice thar I stated "conduit" when referring to "fill"?