New consumer unit on TT Supply - whats the regs. -

whitebeetle

Hi , Got to replace consumer unit on my property (to use as my part p assesment !) At the moment its TT Supply (with earth rod) and feeds to the consumer unit through a 100mA RCD. It is only a small cottage and has the following circuits - Garage supply,cooker,2 x socket ring mains,central heating boiler and 1 lighting circuit.

In order to please the part p assesors whats the best way to play it after ensuring the Ze to be less than 200 ohms (i'm working on this !). Is the 100mA rcd ok or do I need to dropdown to 30mA ?

Can anyone tell me / explain the best /cheapest way to fit new consumer unit to meet current regs on a small domestic TT Supply ?

Thanks - Chris.

electricAl

What we offered here... Earth fault loop impedance reading on TT System in domestic premises

...still stands, Chris. The Regs aint changed in 4 days!

Is there a specific question you don`t feel has been answered satisfactorily?



Re: the Q`s in this post; as already stated you`ll need 30mA RCD`s for any bathroom/shower room circuits + socket outlets + for ccts with cables installed in walls at less than 50mm. As that`s likely gonna include your lighting circuits (& you`ll need 2 or more) you`ll require 2 or more RCD devices (could alternatively be RCCB or RCB0) so as to provide discrimination between devices.

Basically, nowadays TT`s are much the same as TN`s in requirements for CU`s

The 100mA is required only for ccts not requiring the `Additional Protection` of 30mA RCDs, would have to be of the `S` type (delayed) for discrimination of devices, & may be done away with entirely if you can meet the applicable criteria listed at table 41.1 of the Regs. (then you adopt TN values)

Seriously mate, you`ll have to read up on the Regs to get thru your assessment, so have a peak now

On the Ze front, while the official figure is min 200ohms, i`m pretty sure the NIC require 100 (which i`d always look to get even tho` i aint with them) so if it`s an NICe assessment you`ll need <100ohms

Hope that clarifies it further for you

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willosparky

like Al said. as long as your Ze is less than 100 ohms and you fit a dual Rcd board (1 80 amp and one 63 amp rcd, both 30mA) you will be fine. if i was you id put the, garage, cooker and one ring on the 1st rcd, the other ring, heating and lights on the other. The MK sentry split load board is a gd one to use.

not clever

Seen as you only have 6 circuits why not put in rcbo's & if you use an insulated cu do away with the 100mA rcd.

willosparky

rcbo's do cost abit more tho but yh that is another option. the mk split load board will come with the main switch and the 2 rcd's.

also make sure the earth to the rod is 16mm

Lenny

My guess is he'll have sorted it by now as the thread is 6 months old.

willosparky

true but was replying just incase also may help someone else with same question

electricAl

Fair enough but accuracy is always appreciated by those looking for help.

The board you are referring to would actually be classed as a `High Integrity` board - not split load which offer some ways Rccb protected and some unprotected - as in 16th Edition.

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Two heads are better than one - even when they`re sheep`s