Load capacity of parallel concuctor circuit

[Alan Lombardi]

An outbuilding on my property is fed by underground conductors running
through PVC conduit from the house. The two sides of the circuit each
consist of three 14 guage stranded conductors running parallel (total of six
14 ga. conductors). There is a single 8 guage uninsulated ground conductor.
Total distance from the 200 amp service panel to the outbuilding is
approximately 60 feet. What is the equalent wire guage of a single conductor
circuit? What load rating in amps can this somewhat unusual set-up carry at
120 VAC? 240 VAC? Is there a standard reference that provides this
information?

Thanks,
Alan

 

[[email protected]]

An outbuilding on my property is fed by underground conductors running
through PVC conduit from the house. The two sides of the circuit each
consist of three 14 guage stranded conductors running parallel (total of six
14 ga. conductors). There is a single 8 guage uninsulated ground conductor.
Total distance from the 200 amp service panel to the outbuilding is
approximately 60 feet. What is the equalent wire guage of a single conductor
circuit? What load rating in amps can this somewhat unusual set-up carry at
120 VAC? 240 VAC? Is there a standard reference that provides this
information?

Thanks,
Alan

This is not legal (paralleling 14ga conductors) but if we suspend the
law for a minute and answer a theoretical question ;
14ga is 1440 circular mills times 3 = 12330 c/m
(table 8 in the NEC)

That is somewhere between #10 and #8 ... say 35a?

You might even push the envelop and say each 14ga is worth 15a but you
get into derating because you have more than 3 current carrying
conductors. Then we have to know what the type of conductor it is.

Bear in mind, after all of this it is still against code to parallel
14 ga wire

 

[Bill Kaszeta / Photovoltaic Resources]

An outbuilding on my property is fed by underground conductors running
through PVC conduit from the house. The two sides of the circuit each
consist of three 14 guage stranded conductors running parallel (total of six
14 ga. conductors). There is a single 8 guage uninsulated ground conductor.
Total distance from the 200 amp service panel to the outbuilding is
approximately 60 feet. What is the equalent wire guage of a single conductor
circuit? What load rating in amps can this somewhat unusual set-up carry at
120 VAC? 240 VAC? Is there a standard reference that provides this
information?

Thanks,
Alan

Only conductors of 1/0 and larger can be paralled with the further
requirements of same length, same conductor material, same size
in circular mil area, same insulation, and terminated in the same manner.

NEC 310-4

Bill Kaszeta
Photovoltaic Resources Int'l
Tempe Arizona USA
[email protected]

 

[Alan Lombardi]

Thanks for the response to my questions. Okay, it's not legal. It's there.
Is there anything essentially unsafe about it so that I might want to change
it?

Alan

 

[SQLit]

Thanks for the response to my questions. Okay, it's not legal. It's there.
Is there anything essentially unsafe about it so that I might want to change
it?

Alan

Other than it is wrong and potentially dangerous.

The NEC rules are not arbitrary there is sound electrical principals behind
the decisions. The NEC is considered the minimum safety requirement. If you
have a fire and something burns down. If the investigator was to find non
compliant wiring, the insurance claim might be voided. Heck they might even
try to prosecute you.

The really sad part is there are folks that will ignore them and "do it
their way".
The biggest reason I know of that the book is getting bigger not smaller.

 

[[email protected]]

Thanks for the response to my questions. Okay, it's not legal. It's there.
Is there anything essentially unsafe about it so that I might want to change
it?

It is discouraged by the code simply because you have an extra level
of complexity and more places for it to fail.
If this is wire in pipe you should pull it out and replace it with the
proper conductors.
OTOH it is also illegal to run multiple circuits to a building so you
are already going to burn in NEC hell. ;-)

 

[Andrew Gabriel]

Thanks for the response to my questions. Okay, it's not legal. It's there.
Is there anything essentially unsafe about it so that I might want to change
it?

Things that spring to mind...

A poor connection at the end of one conductor could lead to
different path resistances and unbalanced current, causing
the others to overheat. In the degenerate case, a complete
failure of one connection will result in the other two taking
all the load.

The circuit protection is going to be inappropriately too
high in the case of a conductor shorting. The impedance of
the thin conductor could limit the current such that the
protective device takes too long to break the circuit and
a fire is started. In some cases of a cable break and short,
the short circuit current could be flowing to the far end
through two of the conductors, and then back to the breakage
through a single conductor, resulting in an excessively long
path all through conductors which are significantly thinner
than the circuit protection is designed for.

Parallel conductors are allowed in the UK, but the circuit
protection is required to ensure each operates safely, which
in this case would probably require a 6-pole ganged breaker.
It is most unlikely this would ever be the cheapest way to
achieve the aim of providing a specified power over the
required distance.