levels of rcd protection on TT system - long post - prepare cuppa first!

[suffolkspark]

An EICR. i know the owner so im sure they would want it all putting right, its just thinking how i can go about it

 

[westward10]

From what you describe it sounds like the installation should be TT or perhaps was TT but this is no longer the case. The submains supplying other buildings which require main protective bonding would require a cpc adequate to support PME bonding and for a swa cable it would have to be a 50.0, 4 core minimum to support 10.0 bonding. As to whether the entire site should be TT and there is a suspicion it may originally have been is not possible to say from a distance. Do you have a copy of GN7 to refer to.

 

[suffolkspark]

It probably once was as the boards dont look very old so it has probably been faffed with, Would the 32A control panels be required to just have 1sec disconnection time on TT?as it would be simple enough to get 30mA protection to the conveyors circuit, but if not i guess id need to fit a30mA rcd within each control panel.

 

[westward10]

You need to complete the EICR and consider remedial ramifications after however I feel you are undertaking a task you may not be competent to do.

 

[suffolkspark]

forgot you cant ask questions on here without being deemed incompetent, ciao

 

[westward10]

Disconnection times have been replaced by rcd requirements in Section 705 for ADS.

 

[suffolkspark]

thanks, I did touch on that in my first loooooooong post
with reference to reg 705.411.1
(i) all circuits supplying socket outlets are indeed covered by 30mA RCD.
(iii) - which requires all other circuits are protected by a 300mA RCD, well they are covered by the 100mA type S, but is this acceptable? I genuinely do not know the answer to that question. - reg 705.422.7 says S type can be used but it does not say if that s also acceptable for ADS

 

[Ian1981]

Your 100mA time delay tripping times are 500ms max and 130ms min.
If it's protecting circuits with a 0.2 second disconnect time this maybe problematic depending on what the s type trips at.
with a 300mA rcd the max tripping time is 300ms and when testing the rcd needs to trip really below 200ms for a 0.2 disconnect time for circuits upto 32 amp.

 

[westward10]

The 100ma s type will provide a better level of fault protection. Have you decided if it is agricultural.

 

[suffolkspark]

its, as you say agricultural by definition, and that does include processing facilities according to the definitions in the BYB.

the type S went out in 176ms but this is with it having 0.2 ze as it is at present, I cannot confirm how quickly it will operate if it is on TT.

The thing getting me in a tangle now is the discon times, in the agricultural section there is no mention of the 0.2/1sec times only the level of rcd protection, as post #16