SWA Carrying DC - Correct way to earth

[Tim-Cx]

I know PV installers sometimes use SWA to carry DC into the house especially when the PV is ground mounted.

Can anyone help me understand the correct way of doing the following:
1) Earthing the SWA armour, should this just be connected to the house earth as it would for AC or something else, I have been told it can be left floating but would like to know if this is correct.
2) Assuming the voltage and current are within the cable spec is it OK to run 2 separate PV strings via a single run of 4 core SWA.

Thanks

 

[James]

It is NEVER ok to leave the armour of swa cable floating, it needs to be bonded to earth.

 

[Tim-Cx]

It is NEVER ok to leave the armour of swa cable floating, it needs to be bonded to earth.

Thanks James and just to be completely clear is this is definitely true for for SWA carrying DC ? If was for DC specifically that I was told it could float as apparently normal earth would provide no protection.

 

[Electro-tech]

In my opinion 1. Earthing at the inverter for DC fault protection .
2. As long as the loads are balanced surely no different to 3Phase.

 

[James]

In my opinion 1. Earthing at the inverter for DC fault protection .
2. As long as the loads are balanced surely no different to 3Phase.

2. No need for any sort of balanced loads, just ensure the current is less than the cable rating for any core.

 

[davesparks]

Thanks James and just to be completely clear is this is definitely true for for SWA carrying DC ? If was for DC specifically that I was told it could float as apparently normal earth would provide no protection.

Why would DC be any different to AC?

What would make a difference is whether or not the DC supply is connected to an earth reference or if it was an isolated supply.

 

[davesparks]

2. As long as the loads are balanced surely no different to 3Phase.

Can you explain your logic here as its not making much sense at the moment.

3 phase AC and DC are quite different

 

[Tim-Cx]

Why would DC be any different to AC?

What would make a difference is whether or not the DC supply is connected to an earth reference or if it was an isolated supply.

The electrician that told me said that if the cable was damaged that the DC would probably arc and and that the earth connection would make no difference.

I asked the question here as I don't really understand it and I want to know the right way of doing it.

 

[plugsandsparks]

What should happen is the inverter detects leakage of DC to earth (there is only one earth, lol) and shut down

 

[davesparks]

The electrician that told me said that if the cable was damaged that the DC would probably arc and and that the earth connection would make no difference.

Are you sure they are an electrician as that sounds like they lack an understanding of some basic science.

 

[Tim-Cx]

Are you sure they are an electrician as that sounds like they lack an understanding of some basic science.

Yes definitely an electrician and highly regarded at that, incidentally I am not an electrician but I have a science degree and I am not sure how this earthing would protect in this situation either.

I am happy to accept the guidance given here that SWA armour should always be earthed.
I understand that the inverter should be able to detect an imbalance and shut off.

BUT if it is daylight and the PV panels are producing power the cable will still be energised at a high voltage, assuming that the inverter has shutdown the voltage and current will be on the house earth but nothing will break the circuit and therefore there will be no protection. What am I missing here? this is why floating the armour as the electrician has said seemed sensible to me and its why I asked the question here.