Solar cable runs from roof space to plant room on ground floor.

[jimseng]

Hello.

I am planning on bringing the 2 strings +/- cabling through the roof into my loft space. It is an in roof system and I believe there is room to bring the cables in via two cable entry housings mounted underneath the last panels in the strings. I am planning on using PV cabling with MC4 connections to the last solar panels in the strings, through the roof via the entry housing into a connection box. I think it would be sensible to put the SPDs for the solar in the connection box, two breakers and then on to the ground floor plant room to the inverter.

In the loft space the cable run will be in conduit. Does it need to be metal or can I use plastic?

 

My house, which is still in build has a 45mm service void on top of the insulation membrane. Are there any specific rules about running the cabling through that, i.e. further mechanical protection?

I am probably going to be running this cable in way before the ac first fix happens.

[BotusBuild]

Plastic conduit will be fine.

Is the 45mm void just under the roof tiles? I would put the cable in conduit for extra protection.

[jimseng]

Quote

Is the 45mm void just under the roof tiles?

I was referring to the whole house having a 45mm  battened service void behind the plasterboard  for all electrics and plumbing. I'm asking what would be the correct method for getting two runs down to the plant room once it exits the loft space. Is it adequate to follow safe zones in the service void down two floors or am I expected to afford extra mechanical protection for the solar cable.

 

[JohnMo]

I would bring the cables to a multi pole DC isolator on the outside of the house, for ease of access in case of a fire. Then run the rest of the DC to your inverter.

 

Run cables in service void but I would want something to you or someone else drilling a holes later and hitting a DC cable. So in save zone with metallic shield so something like 

https://www.screwfix.com/p/deta-tte-37mm-galvanised-steel-channel-2m/826VT?tc=TA5&gclsrc=aw.ds&gad_source=1&gad_campaignid=22599672207&gbraid=0AAAAAD8IdPyi10Bx2zrVz5Z9Lr6xcezkw&gclid=CjwKCAiA_orJBhBNEiwABkdmjHstK7DySAtkOoGd1V-4dnj9I9QLc64xIKDU339IXlACKlvaonv5AxoChkYQAvD_BwE

[Nickfromwales]

The regs have changed a fair bit here for DC runs in domestic dwellings, so on the last one (summer '24) I ran galv conduit internally to convey the 2x red and 2x black 4mm DC feeds from the roof to the rotary isolators in the GF plant space. Best to double-check with an up-to-date installer. If you need one let me know as I have a very good solar chap who works nationwide.

[jimseng]

Quote

The regs have changed a fair bit here for DC runs in domestic dwellings

This may be a stupid question but can anyone guide me to where I can find these regs?

[Dillsue]

Lots of the wiring regs are open to interpretation and judgement of the spark/designer of the wiring system so if your expecting/wanting the spark who wires your house to include the DC cabling in his installation cert then probably best to take their advice on how they'd like to see the DC cables installed??

[Mattg4321]

7 hours ago, JohnMo said:

I would bring the cables to a multi pole DC isolator on the outside of the house, for ease of access in case of a fire. Then run the rest of the DC to your inverter.

 

Run cables in service void but I would want something to you or someone else drilling a holes later and hitting a DC cable. So in save zone with metallic shield so something like 

https://www.screwfix.com/p/deta-tte-37mm-galvanised-steel-channel-2m/826VT?tc=TA5&gclsrc=aw.ds&gad_source=1&gad_campaignid=22599672207&gbraid=0AAAAAD8IdPyi10Bx2zrVz5Z9Lr6xcezkw&gclid=CjwKCAiA_orJBhBNEiwABkdmjHstK7DySAtkOoGd1V-4dnj9I9QLc64xIKDU339IXlACKlvaonv5AxoChkYQAvD_BwE

That metal capping would barely stop a 5 year old with a sharp crayon. A drill or nail will go straight through it

 

Needs to be steel conduit or 3mm plate or something in front of it. 

[JohnMo]

1 hour ago, Mattg4321 said:

That metal capping would barely stop a 5 year old with a sharp crayon. A drill or nail will go straight through it

 

Needs to be steel conduit or 3mm plate or something in front of it. 

Well there you are then

[Nickfromwales]

3 hours ago, Dillsue said:

Lots of the wiring regs are open to interpretation and judgement of the spark/designer of the wiring system so if your expecting/wanting the spark who wires your house to include the DC cabling in his installation cert then probably best to take their advice on how they'd like to see the DC cables installed??

The competent person has the final say, so +1 to this.

 

4 hours ago, jimseng said:

This may be a stupid question but can anyone guide me to where I can find these regs?

Who's the installer? Ask them, as anything else is conjecture or opinion, even regs are bendable or get garnished with a bit more belt & braces.

 

1 hour ago, Mattg4321 said:

That metal capping would barely stop a 5 year old with a sharp crayon. A drill or nail will go straight through it

 

Needs to be steel conduit or 3mm plate or something in front of it. 

You must live in a rough area if the 5 year olds are running around with TCT tipped Crayola's lol. 

 

1 hour ago, JohnMo said:

Well there you are then

He doesn't mean it, he prob got beaten up by the kids and his crayons nicked  

[jimseng]

40 minutes ago, Nickfromwales said:

Who's the installer?

For the DC and solar side, me. The electrical contractor is doing everything up to the inverter and the load output side. I'm getting my ducks in a row. 

Edited 16 hours ago by jimseng

[Nickfromwales]

6 hours ago, jimseng said:

For the DC and solar side, me. The electrical contractor is doing everything up to the inverter and the load output side. I'm getting my ducks in a row. 

Can you ask their advice and then the whole install will be more aligned?

 

Basically as soon as the DC strings leave the roof and enter the building you’re into protecting them, big time. 

There’s no protection at this stage from high voltage DC, which is nasty stuff. 
 

Usually, before the aforementioned shakeup, we’d fit rotary isolators in attics or eaves or cupboard spaces to convert the strings to SWA, and then run that to the plant rooms / inverter elsewhere. On the one I mention I was told that would no longer suffice, so I had to run 25mm galv conduit from the ceiling void to the plant room and put the isolator on the end of the conduit; from there I imagine high impact pvc conduit or trunking would suffice (not sure what was actually done on this particular clients project as I left after 1st fix). 

[Alan Ambrose]

>>> I think it would be sensible to put the SPDs for the solar in the connection box, two breakers and then on to the ground floor plant room to the inverter.

 

The regs may not be totally clear, but I believe there’s a qn re DC isolators before the inverter. See e.g.

This text and audio (there’s a video too) is one year old;

https://electricalnews.efixx.co.uk/1978879/episodes/14269857-don-t-install-dc-isolators-on-solar-electricians-warned

 

This video quotes the regs but is 2 years old;

 

 

Edited 6 hours ago by Alan Ambrose

[Nickfromwales]

Seems to be very few instances though?

 

Ive been quite intensively ‘around’ a respected member of the STA and a major supplier (German gear) and I’ve not heard any of them over the years mention panels going en-flambé or DC isolators doing likewise.

 

If these are disconnected under load then expect the worst, but that’s damage done in ignorance by dimwits or idle thumbs.

[jimseng]

So according to the latest guidance, don't fit DC isolators as they are a fire risk, except do fit them because the fire brigade like to isolate the PV when tackling a fire. What fun!

Having climbed back up the scaff and looked at it again it is a really easy vertical run down from the roof to the plant room posi joists so fitting trunking should be easy.

[Nickfromwales]

14 minutes ago, jimseng said:

So according to the latest guidance, don't fit DC isolators as they are a fire risk, except do fit them because the fire brigade like to isolate the PV when tackling a fire. What fun!

Having climbed back up the scaff and looked at it again it is a really easy vertical run down from the roof to the plant room posi joists so fitting trunking should be easy.

PVC trunking? 

[JohnMo]

14 minutes ago, jimseng said:

So according to the latest guidance, don't fit DC isolators as they are a fire risk, except do fit them because the fire brigade like to isolate the PV when tackling a fire. What fun!

For me if the house was on fire and it's a sunny day, would a firefighter be able to make safe the PV array without entering the house. If not, I would add a suitably rated external DC isolator in an accessible position.

 

If the inverter is outside and accessible and has an inbuilt DC isolation switch, you really shouldn't add an additional one, according to the rules.

 

That's my view, may different from others.

[jimseng]

@Nickfromwales PVC trunking? Does that fit with:

Quote

Basically as soon as the DC strings leave the roof and enter the building you’re into protecting them, big time. 

PVC would be cheaper but it is only a 3m run straight down into the posi joists and then on to the inverter wall.

[Beelbeebub]

Isn't there a DC specific SWA cable now (the regular SWA not being compliant for DC)? 

[JohnMo]

46 minutes ago, Beelbeebub said:

Isn't there a DC specific SWA cable now (the regular SWA not being compliant for DC)? 

I found this out a year after I installed mine. PV ultra cable is what you need now

[Nickfromwales]

2 hours ago, jimseng said:

@Nickfromwales PVC trunking? Does that fit with:

PVC would be cheaper but it is only a 3m run straight down into the posi joists and then on to the inverter wall.

Big time doesn’t mean in pvc   Heavy gauge conduit or galv trunking.

 

24 minutes ago, JohnMo said:

I found this out a year after I installed mine. PV ultra cable is what you need now

What he said. First time I’ve heard of that cable tbh. Every day is a school day. 

[jimseng]

That PV ultra cable seems to solve many problems. Good tip!