TT help needed!!!

[eskimo39]

Beaver74 I am only on the first year of a three year course.

As stated in the post "Ohms law is our third module starting in January and was just curious as to how I could use it" As I am sure some of you will be aware there are 9 modules alone in our first year before they allow us on to NVQ 2 & 3.

The comment in question to uksel was of genuine interest. I joined this forum for support and (hopefully) guidance. I am not some guy who has done a six week "Intensive" course and now think I know it all, I am a member on here to assist my development and hope in the future I will be able to post answers to help others.

 

[KFORDHUNTER]

I have a question about TT systems, i have just done a rewire on a bungalow, and have installed an earth rod, all readings are good, have installed a high integrity 17th edition board, single rcbo for smoke alarms then split 30ma dual rcd for rest of bungalow, i think that is all you need to do, am i right to say that due to every circuit being protected by 30ma rcd i do not need to oversee the main incomer on a 100ma time delay.

Replies appreciated.

 

[montybaber]

Beaver74 I am only on the first year of a three year course.

As stated in the post "Ohms law is our third module starting in January and was just curious as to how I could use it" As I am sure some of you will be aware there are 9 modules alone in our first year before they allow us on to NVQ 2 & 3.

The comment in question to uksel was of genuine interest. I joined this forum for support and (hopefully) guidance. I am not some guy who has done a six week "Intensive" course and now think I know it all, I am a member on here to assist my development and hope in the future I will be able to post answers to help others.

dont worry Eskimo asking questions will make you a much better sparkie, and I know when you are you will be a lot more helpfull than a few posts on this thread have been

 

[prideofengland]

1) Ze needs to be less than 200 ohms or 100 ohms if your in the NIC.
2)Cable size should be half the size of the phase conductor or calculated using the adiabatic equation: S=_/I²t [FONT=Times New Roman, serif]٪ k[/FONT]
3) Generally its better to go deeper to lower your reading than adding more rods. You can get rods from the wholesalers with a threaded end that allows you to add another rod to it, a ferrule protect the thread from hammer dammage, someone posted a link to it about a month ago.

hope this helps

 

[andy pandy]

if your strugling to get a good earth path for a rod try putting marconite round it this will enhance the earth reading. Try google it will tell you all about it. Allso the chap who has used rcbos to protect smoke alarms, i think rcbos are not required unlless any of your wiring on the smoke circuit is burried less than 50mm below the surface.

 

[SCOL1]

I have a question about TT systems, i have just done a rewire on a bungalow, and have installed an earth rod, all readings are good, have installed a high integrity 17th edition board, single rcbo for smoke alarms then split 30ma dual rcd for rest of bungalow, i think that is all you need to do, am i right to say that due to every circuit being protected by 30ma rcd i do not need to oversee the main incomer on a 100ma time delay.

Replies appreciated.

You are right,if you were installing a metaclad board then you would have to install an RCD on tails to board.As you are using a high integrity board then you dont need to as you already have 30ma protection on all circs.

 

[eskimo39]

Why do you need 100A Time delay on the tails to a distribution board? I thought if the board was fully protected by RCD and RCBO's the 100A breaker would never trip before them.

Is it to protect any metallic parts of the board becoming dangerous? Does a high integrity board have no metallic parts?

Sorry for been so dumb

 

[uksel]

i think he is concerned asbout covering the requirement to have a TT system to be protected by a 100mA time delay RCD

i would suggest installing the 100mA time delay RCD to comply, as although in practice it is highly unlikely each circuit could in theory have a leakage of 20mA, no RCD's will trip yet there could be 240mA running through earth in a 12 way CU.

Eskimo, my apologies if i was rude, i assumed you were making a response to something said in another thread.

 

[eskimo39]

Don't worry about it. I just really was curious. I have been having a good read up on ohms law this morning. Have found 2 different charts. 1 a triangle with V,I,R and the other a circle with P,I,V,R. Not sure what the difference is but it is certainly interesting reading.

 

[uksel]

one allows for Power calculation (measured in Watts, like a lightbulb)

the other is the basic ohms law V=I.R

 

[beaver74]

Beaver74 I am only on the first year of a three year course.

As stated in the post "Ohms law is our third module starting in January and was just curious as to how I could use it" As I am sure some of you will be aware there are 9 modules alone in our first year before they allow us on to NVQ 2 & 3.

The comment in question to uksel was of genuine interest. I joined this forum for support and (hopefully) guidance..

eskimo39 i was'nt being rude i was just statting that ohms law in my apinion should be one of the first thing to learn as almost every thing revolves around this in some way
and i did miss read the 3 years