TT systems. Bonding in bathrooms

by Steve on March 22, 2009


Does the dispensation in Regulation 701.415.2 to omit supplementary bonding in a bathroom apply to TT systems?



Yes it does apply to TT systems.

Regulation 701.415.2 states that supplementary bonding may be omitted where:

  • i) All final circuits in that location comply with 0.4 sec disconnection

  • ii) All final circuits in that location are protected by RCD

  • iii) Main bonding to extraneous conductive parts is intact.

In this case TT systems are treated in the same way as TNC-S & TNS.



{ 5 comments… read them below or add one }

Bud Barkley May 14, 2015 at 09:58

Hi, this confused me too, but after reading I think you’ll find the same conclusion as me.
The disconnection time in a T.T. system is dependant on the R.C.D. Using the 50volt rule.
50/0.03 = 1667 ohms to give 0.2 and 1 second disconnecion time
So if all circuits are protected in the bathroom by .r.c.d’s. we comply with the disconnection time regs.
Personally I think rcbo’s are best in a T.T. system , isolating on both short circuit and earth leakage.
All the best,
Bud Barkley

Editor January 9, 2012 at 16:22

Hi Jim. Yes, there’s a lot of stuff on here now. It’s been a little and often process over about 3 years. Hope you find it useful. -Steve.

jim lawrence January 9, 2012 at 00:22

like the set up of your blog did it take long

ian johnstone July 20, 2011 at 21:50

yep i think you are correct regarding a TT install.

Micelec June 1, 2011 at 17:57

Regarding TT systems and bathroom bonding !!
701.415.2 states that bathroom bonding can be omitted providing all 3 requirements are met.
(i) All final circuits of the location comply with the requirements for automatic disconnection according to Reg. 411.3.2
(ii) All final circuits of the location have additional protection by means of an RCD in accordance with Reg. 701.411.3.3
(iii) All extraneous-conductive-parts of the location are effectively connected to the protective equipotential bonding according to Reg. 411.3.1.2
In my opinion item (i) will probably not be met due to the usually high Zs readings obtained because of the TT system. ie rod resistance + R1 +R2 is usually greater than rated Zs of the circuit device eg. 1.15ohms (corrected value) for a 32A mcb BS 60898
therefore because one of the 3 items cannot be met, then supplementary bonding will be required. (Remember the RCD is there to give additional protection)
I would welcome anyone’s thoughts on this subject.

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