How do I design the circuit for baseboard heaters?

Question

I am designing the circuit(s) for my basement apartment (cca. 800 sq ft) baseboard heating solution. I am planning to buy Berko HBB Series heaters and distribute them as shown in the below table. All have a voltage of 240/208.

Location        Model       Length(in.) Watts       Amps
-----------------------------------------------------------     
Living Room     HBB1504     70          1500/1125   6.3/5.8             
Bath            HBB504      28          500/375     2.1/1.8             
Bedroom         HBB1254     58          1250/938    5.2/4.5             
Hallway         HBB754      34          750/563     3.1/2.7

My questions are:

1. Should I split them into two circuits (living room and bathroom in one, bedroom and hallway in the other) or is it OK to keep them all on one circuit?
2. Is the voltage a factor in determining the wire gauge? I know that the amperage is. E.g. if I split them in two circuits so that each circuit bears less than 10A each, can I go with AWG 14/3 even though the voltage is double than usual? Or simply put, which AWG should I use for either scenario from question 1.?

I have an extensive experience as a DIY electrician, I have pretty much rewired most of my house and have set up one 240/120 circuit for my dryer (used AWG 10/3). But this is considerably lower amperage so I am not sure what AWG to use.

Answer 1

Sizing conductors and breakers

Almost all wire you can buy will be rated at 600 volts, so you won't have to worry about voltage when sizing wires. What really matters is current. Your wires will be sized to carry enough current for the load, and your breaker will be sized based on the wire used.

When installing electrical devices, it's always a good idea to check the manufacturers installation instructions (PDF). In this case, it has this to say...

As the table shows, you can connect up to 24 amperes worth of heaters to a single circuit. However, if you do this, you'll have to use 10 AWG conductors and a 30 amp breaker. If you only want to use 14 AWg, you can only put 12 amperes worth of heaters on a circuit.

Number of conductors

Since these are 240 volt heaters, you'll only need two conductors (plus a grounding conductor). If you're going to use nonmetallic sheathed cable (Type NM), you'll need AWG/2 with ground, not AWG/3 with ground cable.

Answer 2

You can't load a branch circuit more than 80% it's rated capacity for continuous resistive loads such as heaters. Assuming you are getting 240v supply, there's too much load for a single 20A circuit, you must split the loads. With the split loads, you can run two 14 GA circuits, but only if the breakers are 15A. If your breakers are 20A, you must run 12 GA regardless of the connected load.

When you say your are hoping to use 14-3, all 240v baseboard heaters I've seen in North America do not have a neutral connection, so you only need two conductor cable for each circuit. Check your heater connection requirements before pulling 3 conductor cable, you may not need that extra conductor. You weren't planning on a shared neutral were you? That's only possible with 120v circuits.