Maximum Zs explained

[@jmohammad3762]

Good simple explanation and easy to follow. I'm looking forward to more videos James.👍👍👍

[@JamesCurnowElectricalEngineer]

Thank you, I'm glad you like the video. I am working on more videos and hope to add them soon.

[@JamesCurnowElectricalEngineer]

Please see the link to my Q&A video about maximum Zs kzbin.infoghpjJJrAa6k?feature=share

[@darongharvey4097]

Hi James. Great videos in this series! The gaps in my previously sketchy understanding are filling up. Thanks!

[@JamesCurnowElectricalEngineer]

Thanks Daron, I'm glad you like the videos.

[@JamesCurnowElectricalEngineer]

Please also see my video on where to find the maximum Zs for RCD. I have put a link in the description.

[@razomar-cs7wv]

Thank you

[@darongharvey4097]

Question, James (if you don't mind) as there's something I'm not totally clear on regarding the temperature adjusted values. Here's an example for a 32A 60898 breaker: (230 x 0.95) / 160 = 1.37 ohms (as in Table 41.3 on p62 of the regs) Then adjust for temp: 1.37 x 0.8 = 1.09 ohms (shown as 1.1 in GN3 Table A4 & OSG Table B6) I get that, but when it comes to completing the schedule of test results, the values for Max permitted Zs shown in the examples in GN3 (p126) uses the value before temperature adjustment. So where would we use the temp adjusted value? Do we record it anywhere, or is it purely a reference when we use against Max Measured Zs, and if our measurement in this case exceeds 1.1 (as in Table A4 in GN3 p142 and Table B6 OSG p131) then we could be exceeding the max Zs?

[@JamesCurnowElectricalEngineer]

Hi Daron, Thank you for your message. I'm happy to answer questions. When completing the schedule of test results in an electrical certificate, in the column that asks for the maximum permitted Zs, we would enter the maximum Zs from table 41, but when measuring the Zs we check that it doesn't exceed the value that's adjusted for temperature. As that will ensure that the max Zs isn't exceeded when the temperature rises when the circuit is under load. So to answer your question, if the measured Zs is higher than the temperature adjusted value, it would exceed the maximum Zs. There isn't a column that asks for the temperature adjusted figure, however if you wanted to enter this on the schedule, you could add it in the remarks column next to the circuit. E.g. Zs measured not greater than 0.8 x table 41= GN3 also says that where the value for maximum permitted Zs is taken from another source, other than table 41, we can state this in the remarks column next to the relevant circuit. For example, if you are using a protective device which isn't listed in BS7671 such as an mccb, you can obtain the max permitted Zs from the manufacturer. I hope this helps. Regards James

[@darongharvey4097]

@@JamesCurnowElectricalEngineer Perfect. Thanks for confirming. Once I had written and re-read my question, I felt like I was starting to answer my own question, but now I'm sure. Thanks very much, James.

[@pramodgavit7666]

Best vdo Sir

[@Xxxcappie23]

So after you get your ohm value from the equation, what are acceptable and not acceptable values.

[@JamesCurnowElectricalEngineer]

Hello, thank you for your message. The calculation determines the maximum Zs. So an acceptable measured value would be less than the value for maximum Zs. For example, less than 0.8 x the values in table 41. I hope this helps. Regards James

[@practicalelectrical3837]

awesome!!

[@JamesCurnowElectricalEngineer]

Thank you very much. I'm glad you liked the video.