i have never worked on a TT system, but the job i am on now will be using TT,
Its a large house with a 3phase pme supply and a large detached garage and also detached stable block. i will be feeding the garage with a 3core 16mm swa, then feeding the stable block with a 3core 10mm swa from the garage D/B, now am i right in thinking i have to use an insulated D/B enclosure , or can i use a metal D/B and take the swa straight in to the D/B.
will i have to use a rod at each D/B board or just use the cpc in the 10mm swa ( i think rod at each )
i presume on the garage D/B i will use a 100ma time delay rcd to protect the stable block swa , and at the stable block D/B a 100ma rcd (to protect the D/B ) and 30ma to protect everything else
next question, i understand the Ze at the garage D/B should be less than 200 ohms (nic 100), so just say i got 90ohms, now that will make the Zs way high, i understand about The tabulated values for max Zs for fuses and circuit breakers are for TN systems only not TT systems. For TT the maximum Zs is 50/Ideltan.
when filling out the certs what do you put in the column for max Zs permitted by bs7671( would it be N/A ) and do you put the measured figure you actually got in the max earth fault loop imp column
sorry its a bit long winded but as i said..i have never worked on a tt system b4... am i on the right track , any input is very welcome
Its a large house with a 3phase pme supply and a large detached garage and also detached stable block. i will be feeding the garage with a 3core 16mm swa, then feeding the stable block with a 3core 10mm swa from the garage D/B, now am i right in thinking i have to use an insulated D/B enclosure , or can i use a metal D/B and take the swa straight in to the D/B.
will i have to use a rod at each D/B board or just use the cpc in the 10mm swa ( i think rod at each )
i presume on the garage D/B i will use a 100ma time delay rcd to protect the stable block swa , and at the stable block D/B a 100ma rcd (to protect the D/B ) and 30ma to protect everything else
next question, i understand the Ze at the garage D/B should be less than 200 ohms (nic 100), so just say i got 90ohms, now that will make the Zs way high, i understand about The tabulated values for max Zs for fuses and circuit breakers are for TN systems only not TT systems. For TT the maximum Zs is 50/Ideltan.
when filling out the certs what do you put in the column for max Zs permitted by bs7671( would it be N/A ) and do you put the measured figure you actually got in the max earth fault loop imp column
sorry its a bit long winded but as i said..i have never worked on a tt system b4... am i on the right track , any input is very welcome