Discuss Stick to TT or go PME? in the Electrical Forum 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

FatAlan

-
Trainee
Esteemed
Reaction score
1,827
Ok, so you have an old non RCD protected domestic installation on a TT earthing arrangement.
Would it be preferable to upgrade to PME if available by the DNO or stick to TT and protect with up front 100mA RCD if the Ze was ok via the rod?
 
PME every time if available. i prefer to rely on MCBs for fault protection than some skittish RCD that some snotty-nosed kid has spilt orange juice/coke/superglue into.
 
Alan - does the existing TT installation have an 'up front' voltage trip at least ? If not and unless the Ze is very low it's potentially lethal.
 
Yep that's the one, very odd to find an old TT installation without one [unless already replaced by an RCD] so the Ze must be really low or it's well dodgy.
 
I had this argument with the NWEB years ago (long before most of you were born). A TT supply the lecky board wanted to make PME, no bloody way! My reasoning, they were wanting to use my “earth nest” for free. It was far better than their puny rod.

UKPN tried the same trick years later on an 11kV system. The earth nest was 100’s of cast iron piles driven eight foot in to the ground. Somewhere in the order of ½ a mile feet squared in area.
 
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.
 
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?
 
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.
 
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.
 
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.
 
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? :cool:
 
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? :cool:
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.
 

Reply to Stick to TT or go PME? in the Electrical Forum 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

Electrical Forum

Welcome to the Electrical Forum at ElectriciansForums.net. The friendliest electrical forum online. General electrical questions and answers can be found in the electrical forum.
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