EICR 100ma RCD TT systems

[westward10]

BS7671 does not specifically state an rcd must be used for fault protection in a TT system although it is preferred. An overcurrent protective device may be used alone provided a suitably low value of Zs is permanently and reliably assured, see Regulation 411.5.2.
In an era when BS3036 semi-enclosed fuses were the norm then a 5A fuse in todays standards has a maximum Zs of 9.10 ohm.

 

[Strima]

I thought we’d arrived at it being ok to use a tails gland and tails clamp and bring the tails straight in?

As far as I'm aware this is acceptable. It best be as it's what I do... ?

 

[loz2754]

I might be misunderstanding your point.
Lots of properties near me are TT with double insulated tails going into a plastic CU with an RCD main switch.
Come the day these are upgraded to an new and obviously metal CU, I thought we’d arrived at it being ok to use a tails gland and tails clamp and bring the tails straight in?
A while back there was a debate that an up front RCD would need metal containment in 18th and the problem simply moved.
Or have I misremembered the conclusion from the pages of debate?!

I think what I meant to say is that you would have to take extra precautions to mitigate the possibility of a live to earth fault occurring within the consumer unit, if the consumer unit is metal, and the tails are not RCD protected. As opposed to not worrying about it with a plastic consumer unit. My apologies for not typing out what was in my brain!

 

[westward10]

Pre metal consumer unit it was a big no no to fit a metal enclosure consumer unit without rcd protection to its supply on a TT but now it seems okay, the times a changing.

 

[Strima]

Pre metal consumer unit it was a big no no to fit a metal enclosure consumer unit without rcd protection to its supply on a TT but now it seems okay, the times a changing.

But how many times did people use tails clamps/glands etc to mitigate the risk?

 

[westward10]

But how many times did people use tails clamps/glands etc to mitigate the risk?

It would not have been considered.

 

[pc1966]

But how many times did people use tails clamps/glands etc to mitigate the risk?

To me that is the key factor - some additional clamping so tails being wagged does not result in them loosening from the incomer, and the entry glands seem the perfect way of dealing with that and the risk of insulation being cut on the case edge.

Also said incomer's screws correctly tightened. And checked after a wiggle.

Even so, if it were me I would still like to see a 100mA delay RCD up-front even with an all RCBO board to eliminate a single point of failure in the electronics.