Stick to TT or go PME?

[l4urence]

If you stayed TT would their be anything wrong with having a 30mA RCBO CU with a 100mA RCD or for that matter split between two 100mA RCDs?

Why would you use 100mA RCD if you have 30mA RCBO’s in the CU.

 

[FatAlan]

Good point. Getting confused with TT systems with up front 100mA RCDs.

 

[FatAlan]

When I can, I change TT CU’s to RCBO’s. I don’t really like one central RCD that trips the entire installation. I don’t really get how the overhead TT line could be changed to PME, certainly not in my location.

SSE have changed a couple for me both on overhead supplies. All they appear to do is check the available Ze. That’s why I asked the original question really as my DNO SSE appear to be quite happy to swap to PME.

 

[l4urence]

Good point. Getting confused with TT systems with up front 100mA RCDs.

Exactly. RCBO’s are the ways to go right now and not just TT - split load boards (for example) belong in the 80’s.

 

[l4urence]

SSE have changed a couple for me both on overhead supplies. All they appear to do is check the available Ze. That’s why I asked the original question really as my DNO SSE appear to be quite happy to swap to PME.

How very bizarre. Not seen that in my neck of the woods, some changing of PME back to TT for EV charging. The world is changing.

 

[FatAlan]

Also with rumours just before the 18th coming out of a move back to requiring earth rods. Was that a sniff of the big boys in the private sector wanting to avoid responsibility for providing an adequate route to earth?

 

[l4urence]

Also with rumours just before the 18th coming out of a move back to requiring earth rods. Was that a sniff of the big boys in the private sector wanting to avoid responsibility for providing an adequate route to earth?

I think you have a point. The issue with PME is the open circuit PEN conductor - hence the requirement for a rod for PV, outbuilding, shed. So if someone gets fried it’s our responsibility not the DNO, why? Smart meters can shed the load by switching off the supply (volatile renewables?) like I said, it’s all changing. I like TT, you know where you are. My only gripe is the need for a type 1 SPD which are not cheap.

 

[Markyd]

How very bizarre. Not seen that in my neck of the woods, some changing of PME back to TT for EV charging. The world is changing.

I think most EV points have to have their own TT in place

 

[l4urence]

I think most EV points have to have their own TT in place

Only if the supply is PME

 

[Wilko]

Hi - domestically where gardeners may cause Ze fading with a spade, I would convert to PME and RCBO.