Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This one, regarding a domestic radial circuit, its consumer unit (CU) and the installation Ze readings, is answered by the ECA:
The prospective fault current (PFC) at the consumer unit line, and the Ze, has been measured and has been recorded to be 7.7kA, as the installation has a very low line and the Ze reading is 0.03 ohms. Note that the property is located directly next to a sub-station - hence the low line Ze reading.
Noting that Crabtree Starbreaker only manufactures MCBs having a maximum rating of 6kA - and they are a bespoke fit - does this mean that I'll have to install a separate consumer unit with an MCB rated at a higher PFC rating?
Also, what is my responsibility to the existing installation, as there is a problem with the 6kA MCBs obviously being under-rated because of the high PFC?
Answer: You may find that the manufacturer will give the consumer unit and breakers a conditional rating of 16.5kA if it is backed up by a BS1361 type 2 fuse. We suggest that you contact the manufacturer to confirm this.
To see many more Q & A in Voltimum UK's Experts Area, please click on the link:
www.voltimum.co.uk/consult.php?universe=consult.index.questions