When a TT Supply enters a building doers it have to go directly into a plastic RCD incoming box before entering a metal CU? Its just the Guy from NIC the other dau said it would be against regs because not supplementary proected by RCD if 1st RCD was in Metal CU
Incoming RCD for TT System
- Thread starter New2Game
- Start date
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There are issues with entering a metal clad CU on a TT - if the tails become damaged (most likely at the point of entry to CU), there is no earth fault protection, and the CU could become live (along with everything else). If the EFL was high, as expected on a TT, the supply fuse would sit happily.
The NIC have a guide which shows a special grommet used to protect the tails on entering a metal clad CU, but I would still prefer an RCD in an insulated enclosure first.......what am I saying.......I would prefer a TN-s or TN-c-s earthing syste first!
The NIC have a guide which shows a special grommet used to protect the tails on entering a metal clad CU, but I would still prefer an RCD in an insulated enclosure first.......what am I saying.......I would prefer a TN-s or TN-c-s earthing syste first!
So if the TT system came from the supply fuses (3Phase) in2 henley blocks, then tails from the blocks into metal CUs, what would be best action to make safe and to NIC guidlines? Would installing a 3 Phase RCD in plastic CU which supplied Blocks be ok? If CU had a 30mA RCD instead of the required min 100mA RCD is that still ok for a Incomer?
If you are only supplying one CU, then do away with the henlys altogether and just have a TP RCD in a seperate insulated encloseure.
You should use a 100mA type S RCD as the incommer so that you provide discrimination between the incommer and the 30mA RCD(s) supplying the sockets.
I have never seen a TP TT supply.
You should use a 100mA type S RCD as the incommer so that you provide discrimination between the incommer and the 30mA RCD(s) supplying the sockets.
I have never seen a TP TT supply.
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plugwash said:
It is, but there are so many muppet sparkies around that I often see a crappy TT install with main RCD - A ****e design for an install.
It depends how big a site you are talking of, the one I was thinking about was only a tiny one with 6 outlets. The 3 phases were split over the 3 (single phase) posts. The 3 RCDs & 6MCBs were housed in a central location and were connected as a TT system.
Afaik on a larger setup it is acceptable to use a TT system with 100mA or greater type S RCDs for distribution circuits, the outlets must be protected by a 30mA device (iirc 3 outlets max per RCD).
Afaik on a larger setup it is acceptable to use a TT system with 100mA or greater type S RCDs for distribution circuits, the outlets must be protected by a 30mA device (iirc 3 outlets max per RCD).
By far the best method is to use the PME right upto the final connection the 16 AMP SOCKET.
You must not have anymore than 3 sockets per 30mA RCD. Generally, a post/piller will have 2 or 3 sockets, and one RCD. This post will rodded down.
The PME will protect the cables - no RCD on the supply to these cables.
A drawing would be clearer than my explanation.......maybe later.
You must not have anymore than 3 sockets per 30mA RCD. Generally, a post/piller will have 2 or 3 sockets, and one RCD. This post will rodded down.
The PME will protect the cables - no RCD on the supply to these cables.
A drawing would be clearer than my explanation.......maybe later.
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