Thread: Low Draw Appliance Distribution

I'm with a plumbing/mechanical contracting company in the San Francisco bay area. We're working on a project at a luxury apartment building installing a bank of 10 tankless condensing water heaters. Each heater pulls roughly 2.5 amps at full load. From a cost and functionality view, it makes little sense to install outlets at each heater, which we've done previously on smaller installations. Instead of installing fused switches at each unit, we'd like to build a small distribution panel using 3A, 2 pole DIN mount breakers and bus bars in a lockable wall mount NEMA enclosure allowing us to run everything on a 30A circuit. It would be similar to a pump control panel. All of the heaters would be hardwired.

I'm unaware of any California electrical codes prohibiting such an installation, but is there anything we should look out for?

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This would be something better addressed with the local building official, and not on an internet forum where you may not get accurate information.

Originally Posted by Richard Tani

We're working on a project at a luxury apartment building installing a bank of 10 tankless condensing water heaters. Each heater pulls roughly 2.5 amps at full load. From a cost and functionality view, it makes little sense to install outlets at each heater, which we've done previously on smaller installations. Instead of installing fused switches at each unit, we'd like to build a small distribution panel using 3A, 2 pole DIN mount breakers and bus bars in a lockable wall mount NEMA enclosure allowing us to run everything on a 30A circuit. It would be similar to a pump control panel. All of the heaters would be hardwired.

All the above and "From a cost and functionality view" would make it "little sense to install outlets at each heater"? Seems to me that from a cost and functionality point of view, installing receptacles would be the practical and inexpensive way to go, that is, provided the water heaters are listed for cord and plug connection.

I tried to download the installation instructions but nothing would come up on the specifications page, not sure if they are just having a temporary glitch in their server or not.

If they are not listed for use with cords and plugs, then hardwired would be the only option available anyway. Even then, though, seems that "From a cost and functionality view", installing 5 on a 20 amp circuit with 5 15 amp receptacles, and the other 5 on another 20 amp circuit with another 5 15 amp receptacles would be the way to go. The combined max load on each 20 amp circuit would only be 12.5 amp from your numbers.

Being as I could not download the installation instructions, I don't know what the manufacturer specifies for minimum circuit ampacity or maximum overcurrent protection from a listing, labeling, and manufacturer's installation instructions.

Just offering some food for thought.

I'm sorry, I should have mentioned that the customer requires independent overcurrent protection for each unit. In the event of a short they don't want half of their capacity going down.

Originally Posted by Richard Tani

Instead of installing fused switches at each unit, we'd like to build a small distribution panel using 3A, 2 pole DIN mount breakers and bus bars in a lockable wall mount NEMA enclosure allowing us to run everything on a 30A circuit. It would be similar to a pump control panel.

Originally Posted by Richard Tani

I'm sorry, I should have mentioned that the customer requires independent overcurrent protection for each unit. In the event of a short they don't want half of their capacity going down.

Okay, but the control panel you are contemplating would likely require Field Evaluation by a Field Evaluation Body (similar to, but different than, a NRTL, although many NRTL also do Field Evaluations too).

Unlike listing and labeling (UL, ETL, etc), field evaluation is only good for the item as evaluated and in that location. Like being listed in which any changes voids the listing, any changes voids the field evaluation. Unlike being listed, a listed product can be installed wherever the listing allows it to be, whereas a field evaluation is voided if the product or item is even moved to another location in the same room - a field evaluation is that specific.

For the cost of a field evaluation you could install a 15 amp circuit and receptacle for each of the 10 units, and have hundreds, if not thousands, left over. Even if you wanted to install an inline fuse to reduce the overcurrent protection from 15 amp (which is to protect the circuit) to 3 amp (to protect the equipment).

DIN rail breakers are not approved for branch circuit breakers in the US, believe they are considered supplemental circuit breakers, they really are best suited for use in the 50 Hertz world, IMHO.

A properly designed circuit should not create a tripping hazard even if half the units were on one circuit. What issues are they foreseeing that they want each unit protected?

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A properly designed circuit should not create a tripping hazard even if half the units were on one circuit. What issues are they foreseeing that they want each unit protected?