How Many Thermostat Wires in One Hole.

Alan (California Radiant) Forbes

We have a job in San Francisco with 25 zones. I know: Crazy, but the owner is a techie and likes choices.

I usually drill 3/8" holes for thermostat wires and run one wire per hole, but with so many thermostats, it makes more sense to drill one or more large holes for all of them; 1-3/8" size since that's a common drill bit for us.

I know that sensor wires should run alone, but is there a problem grouping thermostat and manifold actuator wires?

Jamie Hall

Are the manifold actuator wires at line voltage or 24 volts? If line voltage they shouldn't (depending on code, flat out mustn't) be run in the same hole, never mind conduit.

Alan (California Radiant) Forbes

Yes, Jamie: All 24 volts.

mattmia2

Not to drift too far in to the weeds, but I thought for line voltage wiring there were some exceptions to the fill derating requirements to account for all the cables being on the same circuit so collectively they could only be carrying the ampacity of the circuit so they did not need to be derated when combined.

Zman

As long as they never want to convert to a system like Tekmar TN4 where the system communicates through the wire you should be OK. On high-end jobs, running shielded cable is a good idea to future-proof the installation.

Jamie Hall

mattmia2 said:

Not to drift too far in to the weeds, but I thought for line voltage wiring there were some exceptions to the fill derating requirements to account for all the cables being on the same circuit so collectively they could only be carrying the ampacity of the circuit so they did not need to be derated when combined.

True -- but only if they are in fact all on the same circuit and of the same voltage. You can have two or more circuits in a conduit (depending on fill, of course), but only if the are complete circuits -- that is one or two hots and a neutral.

But never different voltages.

HVACNUT

If your using say 5 transformers, I would at least bundle them that way. 5 sets a piece. And label label label.
On jobs like this, do you typically leave a field wiring schematic behind? 

mattmia2

Zman said:

As long as they never want to convert to a system like Tekmar TN4 where the system communicates through the wire you should be OK. On high-end jobs, running shielded cable is a good idea to future-proof the installation.

Shielded cable would insure against any weird discoveries like hey this model thermostat makes some hash that normally isn't a problem but when you couple the lines to several together by running them in parallel or to a different model that hash interferes with the other t-stat. This was my concern, not about heat which is what the rules in the NEC for line voltage are concerned with but about discovering some weird interference.

mattmia2

Oh, also, Avixa and Bicsi have rules for fill for low energy wiring, i would look there if you want to figure out how many cables you can physically pull through a series of holes without damaging them.