Recent content by richardindorset

Need to work out how I'm going to the NVQ part....

Well I managed to get a distinction in the C&G 8202 level 3 written final exam, despite C&G's odd questions! So thanks to all the people on here who chipped in with answers to my questions!

Yes, I understand that power factor is a factor to take into account, but the exam question clearly expects the student to know that discharge lighting needs a 1.8 factor for breaker current selection, without stating a value for power factor. There doesn't seem to be an obvious regulation in...

exam question.

Yes, I did find it in the OSG eventually, tucked away in a note on diversity. A question on what breaker to use for discharge lighting was in a past C&G exam and our course covers a lot of lighting but not what factor to use. I tried looking up 'discharge' in the 18th and reading the outdoor...

Not just me then!

Thanks! Tried the index, couldn't find it in the 18th edition. Will keep looking!

Is there a source for the 1.8 factor used for picking a breaker for discharge lighting circuits? Is it in BS7671?

Just wanted to confirm my understanding here. Ignoring power factor for the moment, I know that the formula used to get current from total power is total power/(root 3 x phase voltage) This is the phase current, so we use this for each line cable and fuse, of which there'll be 3. The root 3...

After some more reading I see Zs(m) mentioned. This is the value of Zs measured. So when doing verifiaction of measured Zs, one should always use the values in the OSG, or the BS7671 regs book * 0.8 (80%). This makes total sense, even if C&G don't seem to do it... One part I am still not sure...

Ah! OK, that makes a lot more sense. So a BS88-2 would be 130A in 0.4 seconds. So 1.344 ohms. Very close to the OSG figure. Reading the Guidance Note 3 book, it suggests four methods to decide if the measured Zs is acceptable.

Todays class ended in a bit of a fiasco trying to work out how to check compliance for measured Zs, when given various protective devices. For example: A circuit is protected by a 20A BS88-2 fuse and measured Zs is 2.08 ohms. Ambient temp is 20 degrees C. I approached this question using the...

Interesting! Thanks. Still think this is a bit advanced for level 3 exams, especially when there's no mention of it in the course notes!

Further to this question, seeing as we're all looking at it here, they ask about earth leakage and leaky PC power suppies. What do they mean "high integrity earth"? If the ring has its own breaker and is an independant circuit, the earth is going to be 'high integrity' anyway? Or is there some...

Well I have the answer sheet and the scoring method. Here's the question: Here's their answer: