Discuss A/C installation "outdoor to indoor" cable query in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:   American Electrical Advice Forum

Zdb

-
Esteemed
Reaction score
496
So I went to a job yesterday where the A/C engineers had upgraded an air conditoning system and fitted new units. I was there just to switch on the power and do the testing and certification on the electrical side of things.

They used the existing supply cable from the old unit (6mm) and MCB (B32).

The bit that confused me was that the cable going from the outdoor unit to the indoor unit was only 1/1.5mm.

Surely this is too small for the 32a MCB or am I missing something?

Please can someone advise as I don't usually get involved in A/C installations.

Thanks.
 
We have got this set up on a job we are on at the moment where a 6.0mm SWA goes to outdoor unit and they have run 1.0mm flex to indoor unit I assume that it is internally fused.
 
the load of the internal unit is a fixed load within the ccc of the 1.5mm or whatever cable is used. therefore overload protection for this cable is not needed.just s/c protection, which is provided by the 32A.
 
All the cable fro condenser to evaporator does is run the fan in the evaorator and is internally protected.
 
Depending on cable type, if the cable is 1mm isn't that too small, according to table 52.3 of the regs?
 
Yes, but perhaps relying on manufacturers spec as its flex (last section of that Table)

True mate. The OP didn't specify what cable it was. That's why I put 'Depending on cable type'
 
True mate. The OP didn't specify what cable it was. That's why I put 'Depending on cable type'
do you mean round or flat? ;)
 
Not sure what the regs mean by 'flexible cable' as all cables are flexible...when you bend them enough....
 
At risk of being a goody two shoes here, but I'm concerned that 1mm may not survive a low Zs sc on C32 (?) without damage if it was already running hot. Perhaps apply adiabatic?
 
For disconnection times quicker than the stated 0.1 seconds given in appendix 3 the let through energy from the manufacturer of the mcb would be needed.
So K2 x S2 must be equal to or greater than the I2t let through energy of the mcb for fault protection and tho damage doesn’t occur to the cable.
As an example from hager a type b and c I2t value for a 32 amp mcb is 29kA for a 6ka device.
S0 1.5mm should be fine given 1.5x1.5 =2.25 x 115x115 = 29,756.25 so 1.5 mm is protected in this example.

Edit substituting 29kA in the Adiabatic equation gives a size of 1.48mm for compliance so 1.5 scrapes in.
 
Last edited:
As pete said,most of these are fed from an internal board,which has its own protection,applicable to the csa of the cable used. As does the 120W circulatory pump,on a 8kW electric boiler.
 
SY is not suitable for use outside as it has very poor UV resistance and is not water resistant.

After a few years the outer sheath cracks and the steel braid starts to rot.
 

Reply to A/C installation "outdoor to indoor" cable query in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc
This website was designed, optimised and is hosted by Untold Media. Operating under the name Untold Media since 2001.
Back
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock