VOLTAGE CHECKS - SAFE ISOLATION - SINGLE PHASE - THREE PHASE - REVERSE POLARITY - HOW - WHERE - WHAT
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- Опубликовано: 14 май 2024
- There have been many questions on social media about safe isolation tests with specific questions about the voltages to be expected, and the differences between them when testing single phase and three phase boards for safe isolation and before starting work.
And another frequent question concerns reverse polarity - what will reverse polarity voltages look like when the switch is on and what will it be when the switch is off. How do we recognise a reverse polarity circuit?
Many of you will already carry out safe isolation on a regular basis, but for those that are new to the trade, or need a refresher, then we hope that this video will help.
We look at what the measured voltages will be on a good circuit with the power on and compare this to the voltages (or not) that should be expected with the main switch or circuit breaker turned off.
And then we will look at some different reverse polarity scenarios and discuss the dangers of a circuit that is wired incorrectly.
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Visit our RUclips channel where we have many more videos on a wide range of electrical topics.
I love the fact that you do not leave anything to chance and also the way that you build up the explanation from the very basics. I don't think I have missed any of your videos even if I think I will know it all. Why? Again... it is the way you cover all ground and probably your approach is effective for me, so thank you for the effort.
May I ask of suggest you add a detailed video on first fixing of a house wiring for example. Although there might might be some sporadic of that sort here on you tube, your professional approach would be appreciated premendously by quite a few people I know.
Its on the list and will be looked at. Thanks for watching. Dave.
Excellent explanation,
You missed a very important point though, if using a GS38 approved voltage indicator that gives a audible signal be extra careful as this can confuse some people when test an installation that has a
TNC-S earthing arrangement because the earth and neutral are joined the test with give a continuity sound and someone with limited experience could mistake that a a live voltage.
Great video Dave as always.
Thanks for the input. To be honest, I could have talked for two hours just on safe isolation, I have to stop at some point.
Glad you enjoyed it, thanks for the support. Dave.
What is the difference between isolated and switched off? It's a big difference. As an amateur home electrician who worked in the electricity supply industry for far too long I am very aware of Company Safety Rules. [BTW my company used the term, "not live" rather than, "dead"!]
You use "isolated" where I would say "switched off". It's not "isolated" until some physical means to prevent re-energisation has been employed, preferably with a locking device, to which you hold the key. The locking devices employed on MCBs vary. If it is not possible to lock the device then the enclosure needs to be secured or you need to post a person to ensure that re-energisation is prevented.
Safe Isolation is proving it is a dead circuit or installation and preventing the re-energisation. As you say, short of posting a guard, there are limits.
Most important to check for voltage present. Yes I try to follow this rule always. Shutting off main breaker does not mean power is dead. Check your meter with a known voltage first to insure it's working and then check the unknown equipment for voltage. And check your meter again with the known voltage. This is the only way to make absolutely sure you are not going to get caught with electrical shock or arc flash.
Great support, thank you. I always say --- if the circuit isn't dead, you might be.
Hi friend thanks for the informative video
Thank you for watching, appreciated. Dave.
Wonderful
Glad it was useful. Dave.
In a three phase system, my Red Phase to Neutral is 198V, Yellow to Neutral 260V and Blue to Neutral 249V. This happens when the three phase breaker is ON.
When the breaker is OFF, the incoming phases will be normal. What causes this imbalance?
Sounds like a loading imbalance. Can you disconnect the loads and then reconnect one at a time to find out the problem area. Are any of the loads very reactive.
Now I understand. Why dont they teach it like this in college.
Thanks for the great feedback, glad it was useful. Dave,
Your explanation on ‘nominal’ is misleading. You say that the voltage can be between 220 and 240, but most likely to be 230. You state that ‘nominal’ is “just a name we give it”. In engineering parlance, 'nominal' is used when a value is the most likely within a range. Better to say, 'usually' or 'expected', to imply a range and act as a warning. Your use of language needs to be as accurate as your use of a meter. Your vids are some of the best on YT though, especially the graphics.
Thanks for your input.
Wiring Regulations - Voltage by which an installation is designated or known.
Chambers dictionary - In name or thought only but not in reality.
Thank you for watching. Dave.