The IET is carrying out some important updates between 17-30 April and all of our websites will be view only. For more information, read this Announcement

Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 21 replies
  • Subscribers 31 subscribers
  • Views 2973 views
  • Users 0 members are here
Options
You may also be interested in
This discussion is locked.
You cannot post a reply to this discussion. If you have a question start a new discussion

Metal CU, TT earth and wiring for SPD

Former Community Member
Former Community Member

It appears from everything that I have read that for a TT system it's normal to use a metal consumer unit with normal 100A main incoming switch and RCBO's for circuit protection.

This is based on the unprotected live conductors, meter tails and busbar being well protected and supported reducing the risk of fault. Therefore the risk caused by high earth loop impedance and a live conductor contacting the metal consumer unit is very  low.

It also from catalogues etc to be normal practice to introduce SPD's into these CU's along with a circuit breaker to protect them. This means additional wiring which presumably is not double insulated and does not benefit from additional support.

I could avoid the above with an external SPD but that adds cost and just makes the installation more cluttered.

Am I correct that industry believes it's acceptable to use spd's internally on TT protected CU's along with the additional risk the wiring would cause?

Parents
  • 0

    I come across many TT installations here in the sticks. I normally install a time delayed 100mA R.C.D. in an insulated enclosure before new all metal consumer units, and then R.C.B.O.s in the new consumer units. I have had success with this method in all cases but one.

     

    I had nuisance tripping of the 100mA time delayed R.C.D. in a small domestic installation. All circuits tested good and no 30mA R.C.B.O. tripped off, just the pre consumer unit 100mA time delayed R.C.D.

     

    I changed it for a D.P. main switch to avoid continual nuisance tripping. The reason for the tripping is unknown, but the home is near to Bacton where there are large radio masts at the gas terminals. A faulty R.C.D? I don't know. It tested out o.k. during testing.

     

    Z.

Reply
  • 0

    I come across many TT installations here in the sticks. I normally install a time delayed 100mA R.C.D. in an insulated enclosure before new all metal consumer units, and then R.C.B.O.s in the new consumer units. I have had success with this method in all cases but one.

     

    I had nuisance tripping of the 100mA time delayed R.C.D. in a small domestic installation. All circuits tested good and no 30mA R.C.B.O. tripped off, just the pre consumer unit 100mA time delayed R.C.D.

     

    I changed it for a D.P. main switch to avoid continual nuisance tripping. The reason for the tripping is unknown, but the home is near to Bacton where there are large radio masts at the gas terminals. A faulty R.C.D? I don't know. It tested out o.k. during testing.

     

    Z.

Children
No Data

Join us to get the best from IET EngX.

Joining EngX lets you personalise your experience so you stay up to date on the topics that interest you, plus you’ll be able to make connections who are looking to collaborate, exchange ideas and more.

Join us Not now

Community Rules & Guidelines