single pole rcbo's in a tt system

[steptoe]

Techna Double Pole Rcbo Type C 40a 30ma (28-5230)

 

[Sidewinder]

This site shows 2 module for the same part no.

C trip curve 32A rated 30mA Sensitivity,RCBO, C trip curve, 32A,RTEC2C32030,

 

[steptoe]

I know, and if you go to the specs it shows 2 module,!!!

they come in 2 module or single, but they are DP single module if you specify that,!

the pic also shows a c6 for every size you click on, its a pretty shabby site TBH.! but the RCBOs are OK.

 

[Nicky Tesla]

Its all about isolation and when you need it. For eg, you need to put a class 1 light fittings up. You need 2 pole isolation so lets just switch the main switch off. Hang on, its dark, i need to plug in my inspection lamps and charge my batterys and keep the kettle boiling. This would not be possible unless you had a 2pole rcbo or 2pole switch

 

[Evans Electric]

That one is also marked " Test monthly"

What happened to quarterly?

 

[eamonn1983]

Can anyone clear this up as to what we are expected to now do in a tt installation?

thanks

Eamonn

 

[steptoe]

Can anyone clear this up as to what we are expected to now do in a tt installation?thanks

Eamonn

NO

 

[Steve3948]

Can anyone clear this up as to what we are expected to now do in a tt installation?thanks

Eamonn

Well have you read the whole thread, I think it explains everything.

 

[SLIPSHOD & SLAPDASH]

Well i will have a go (Full PPE equipment on) . Putting aside metal/plastic boards etc, To meet BS7671 single pole RCD protection is acceptable if used with a double pole main switch. Thats what i was told by the NICEIC tech helpline 2 years ago. Lots of the 'the NIC said this and that' stories you hear may be specific on the actual situation being discussed at the time, not general comments. However, many electricians work to a higher standard & will only fit double pole Rcd/rcbo's

 

[steptoe]

well, a couple of years ago I put it to my AC assessor, he couldnt answer me,

when I pointed out the pitfalls of SP on a TT he agreed with me that DP would always be required on a TT to comply with 7671,

so, even the NICEIC dont know, depends if there is an E in the day maybe.

---------- Post Auto-Merged at 22:35 ---------- Previous post was made at 22:33 ----------

BTW, it wasnt there and then, He rang me back a few days later with the answer about DP being a requirement, so he musta checked it up,

I dunno, just saying

 

[steptoe]

Can anyone clear this up as to what we are expected to now do in a tt installation?thanks

Eamonn

how dos eamonn, why dont you go introduce yourself,

and tell us all how the rock is at this, one of the finer times of the year,

 

[OnOff]

There seems to be a massive disparity in prices for 2 pole, 2 module RCBOS. I've seen the cheap Chinese brands as low as

 

[Steve3948]

There are some double pole single module RCBOS, although I've never used them.

 

[OnOff]

There are some double pole single module RCBOS, although I've never used them.

Yep, aware of that. Not fussed TBH as to 1 or 2 module as it's a new cu that will go in in an old doorway so board can be as big as is needed. Looking at the multi row boards. Found some that look good are dead cheap but again appear Chinese plus for some reason the site says the 2 / 3 row cu's are only for use in the Repuplic Of Ireland - have emailed the company as to why but they never came back to me on it!

Hager would be the preferred choice but for cost! Probably go Doepke.

 

[Steve3948]

Yep, aware of that. Not fussed TBH as to 1 or 2 module as it's a new cu that will go in in an old doorway so board can be as big as is needed. Looking at the multi row boards. Found some that look good are dead cheap but again appear Chinese plus for some reason the site says the 2 / 3 row cu's are only for use in the Repuplic Of Ireland - have emailed the company as to why but they never came back to me on it!Hager would be the preferred choice but for cost! Probably go Doepke.

Went off Hager a few years back, all got a bit flimsy.

I like to use SqD Qwikline II when price is not an issue, then MK and then BG, in that order.

MK do a stack kit and prices can be thrashed out with merchant.

 

[OnOff]

Went off Hager a few years back, all got a bit flimsy.I like to use SqD Qwikline II when price is not an issue, then MK and then BG, in that order.

MK do a stack kit and prices can be thrashed out with merchant.

As I say I'm looking at a big board with I've had a quote from Doepke who couldn't have bee more helpful, interestingly it seems they're made in Austria:

DIMEF- 36 SPEC c/w Trade Price Each

 

[unphased]

My take on it is, the need for RCD protection on a TT system is mainly to overcome the poor earth fault loop impedance (high Zs). There is no difference to requirements for disconnection times bewtween a TN or TT system, its just that on a TT system the earth rod gives such poor earth resistance (over 1 ohm) that faults to earth won't satisfy disconnection times, hence the RCD requirement. The trip current requirement limits touch voltage to 50V. ie Ra x Idelta n less than or equal to 50V. This is achieved on a TT sytem if Zs is less than 1667 ohms 30mA RCD or 500 ohms on a 100mA RCD. (Notwithstanding max recommended is 100ohms). So the use of RCDs on a TT is mainly for satisfying disconnection times for earth faults. Traditionally (if that is the right word) fault disconnection has been in the phase or line conductor. Hence all fuses in the line conductor. Isolation is not necessary for fault disconnection. Isolation is a requirment for maintenance is it not? Before you put your mits on a circuit it should be isolated.

 

[Sidewinder]

unphased,

Try table 41.1 in the bgb.

 

[unphased]

Thank you sidewinder. ; \ There is a difference between disconnection times between a TN and TT. (0.4s and 0.2s for 230V). The point I was trying to put over is that the RCD is required more for the poor EFLI than anything else. In other respects both TN and TT are indifferent where L/N faults cause disconnection. Is that better explained? I don't know.

 

[Sidewinder]

I knew what the RCD is required for, but yes, now IMHO your point is clearer.

Yes the RCD is required due to the low current due to the high EFLI in a TT system.

Though, if you stuffed say a dozen rods or a mat in on a steel building you could easily et well below 1 ohm.