Mitchell
Active member
Summary
Does the electrical code permit using two smaller-size conductors in parallel instead of one larger conductor.
Detail
I'm in Toronto, Canada and am preparing to buy/run the cable for an OpenEVSE to charge at the full 6.6 kW, and I understand about needing to use #8 wire on a 40-amp 240-volt circuit.
Since the EVSE would be in a garage attached to the house, and in the garage the cable would be exposed, rather than using conduit, I plan on using armoured AC90 (BX) cable all the way from the main panel.
The problem is apparently nobody makes #8/2 (that is, two insulated conductors plus a ground wire) armoured cable, so the usual choice would be to use #8/3 (which is widely available) and simply not use the third conductor.
But I see that #10/4 armoured cable is available, and applying the 80% derating for having more than three conductors in a raceway or cable, each conductor can carry (30 amps x 80% =) 24 amps, so using two conductors in parallel for the L1 and the other two conductors for the L2, this should be allowed to carry up to 48 amps, so the #10/4 can carry more than the 40 amps needed. Not only does this not waste a copper conductor, the cable diameter is less (#10/4 AC90 is only 0.62" diameter, compared to 0.838" for the #8/3).
Another advantage of using #10/4 paired conductors is that #8 solid conductor copper wire has a resistance of 0.6281 ohm/1000', but two #10 in parallel have a total resistance of only 0.499 ohm/1000'. So for my 50' cable run (100' of cable for the loop from the panel to the EVSE and back), the total power lost in the cable due to resistance would be reduced from 47.5 w to 37.8 w, so it would be more efficient too.
But I've been told that while doubling-up conductors is allowed for a service run, it is not allowed on a secondary circuit. I've briefly checked the Canadian and Ontario Electrical Code books (many years ago I knew these well, but only have old versions of them now), and don't see anything about restrictions on using wires in parallel. Does anyone know of electrical code or other reasons for not using two #10 in parallel instead of one #8 conductor.
Does the electrical code permit using two smaller-size conductors in parallel instead of one larger conductor.
Detail
I'm in Toronto, Canada and am preparing to buy/run the cable for an OpenEVSE to charge at the full 6.6 kW, and I understand about needing to use #8 wire on a 40-amp 240-volt circuit.
Since the EVSE would be in a garage attached to the house, and in the garage the cable would be exposed, rather than using conduit, I plan on using armoured AC90 (BX) cable all the way from the main panel.
The problem is apparently nobody makes #8/2 (that is, two insulated conductors plus a ground wire) armoured cable, so the usual choice would be to use #8/3 (which is widely available) and simply not use the third conductor.
But I see that #10/4 armoured cable is available, and applying the 80% derating for having more than three conductors in a raceway or cable, each conductor can carry (30 amps x 80% =) 24 amps, so using two conductors in parallel for the L1 and the other two conductors for the L2, this should be allowed to carry up to 48 amps, so the #10/4 can carry more than the 40 amps needed. Not only does this not waste a copper conductor, the cable diameter is less (#10/4 AC90 is only 0.62" diameter, compared to 0.838" for the #8/3).
Another advantage of using #10/4 paired conductors is that #8 solid conductor copper wire has a resistance of 0.6281 ohm/1000', but two #10 in parallel have a total resistance of only 0.499 ohm/1000'. So for my 50' cable run (100' of cable for the loop from the panel to the EVSE and back), the total power lost in the cable due to resistance would be reduced from 47.5 w to 37.8 w, so it would be more efficient too.
But I've been told that while doubling-up conductors is allowed for a service run, it is not allowed on a secondary circuit. I've briefly checked the Canadian and Ontario Electrical Code books (many years ago I knew these well, but only have old versions of them now), and don't see anything about restrictions on using wires in parallel. Does anyone know of electrical code or other reasons for not using two #10 in parallel instead of one #8 conductor.