Electricians' Guide: Circuit Protective Device Selection

[@davidfalconer8913]

A common fault with certain new items stored in ( damp ? ) sheds , ( air fryers , sandwich toasters etc ... ) , is that damp gets into the element's mineral insulation causing modern house's RCD to constantly trip , the owner might then throw this item away ! .... one trick is to take it to a house with ( old skool fuse box circuits ! ) , run the item for an hour or two , and hey presto ! the RCD no longer trips at the customer's house ..... ( tried - n - tested ) ............ DAVE™ 🛑

[@westinthewest]

3:57 'Professional brands like BG' - I've never heard of this classification. Is there a list of non-professional brands so I can avoid using them?

[@12000gp]

Yeah but what would the industry be without the grass roots leveI amateur brands that just make them for the enjoyment of the game, not for the money.

[@Thats_Mr_Random_Person_to_you]

@3.34 If the boiler load characteristic is 'purely' resistive would kinda depend a little bit on the internals so definitely not ideal to infer as such. I mean its definitely fair that its not purely inductive either cause it wont be. But the exent of the phase change between I and V will depend on the types of pump. Most seem to be AC therefore have an inductance value of some sort (usually low uH)... so depending on the size of the motor it will definitely add an inductive element reducing the PF away from Unity (ie PF of 1, or 100%). Also the low power element need a AC-DC PSU, which will have filter caps on its input lines (Class XY) adding capactance to the load characteristic further reducing the load PF away from Unity. I fully appreciate this is pedantic as hell... the PF is still going to be high as the above elements will only contribute a small amount, but this being a training module, it perhaps needs to be more 'accurate' than a casual video and to say a boiler is a 'purely' resistive load (ie PF of 100%) isn't technically correct. Its gonna be close and (hazarding a guess) have a PF in the order of 80-99%. I would say the load is 'almost entirely resistive'. This is pedantic as hell.... I get that, but this isna training video as part of a CPD certified course. I hope I'm not missing something obvious.....

[@efixx]

It's a fair point, and I debated this point back and forth a lot to be fair, but I think as it's an introductory course I've struck the right balance between being alert to manufacturer's direction and going too far into the finer details. Modifications due to power factor will likely be covered in future training modules.

[@travoltasbiplane1551]

In fairness though... Small controls aside... All of the actual load is resistive. Any electronics are going to be a negligible contribution to the whole. Obviously if there was a stated power factor you should use it but if there was one in this case it will probably say greater than 0.99 if anything and he did say manufacturers instructions should be consulted.

[@deang5622]

I don't think it is a question of striking the right balance. It is easy enough to explain that a heating element made from a coil of wire will have some amount of inductance as it's also a solenoid passing a current and creating a magnetic field. This is quite literally school level. So it can be explained that a heating element has both electrical resistance in order to generate heat, and have some amount of inductance because it's creating a magnetic field. And therefore as it is not a 100% resistive load, the power factor is less than 1. I have just explained it without going in to too much detail and using knowledge which the student already has, or should have. So there is an explanation which is very simple to understand that doesn't go into heavy detail and is factually accurate. How then do you explain an electrical clothes iron which sparks when turned off or unplugged? Doesn't that contain a heating element? What's the cause of that, the resistance element of the load?

[@travoltasbiplane1551]

@@deang5622 because there's enough voltage for the current to jump the gap as the contacts open or close. This happens even with convection heaters. It isn't unique to an inductive load but it is more visible on heating loads because of the current draw. This is such an argument over nothing on this thread it's unreal. None of our designs or calculations are accurate to the level of needing to worry about power factor on resistive loads like this. It's verging on farcical.

[@deang5622]

@@travoltasbiplane1551 And you think that for an iron it only happens as a result of the 230 volts across the contact? Utter nonsense. Ever heard of back EMF's? Do you know what causes a Back EMF?

[@triggsymalone9820]

Real voltage in my area is 243v and its never changed in my 30 year off sparking.. you should always checked your local area voltage 1st..

[@petergrimshaw8291]

3:40 in the video you say if the nominal voltage U0 goes higher it will cause more current to flow? ln = P/U0 if U0 is higher the current will fall. Worst case scenario Ln = 9000/253 =35.6A

[@wackypeace1135]

I think it was just a mistake.

[@travoltasbiplane1551]

Resistive load. Bang the same figures into ohms law.

[@travoltasbiplane1551]

After you've derived a resistance

[@travoltasbiplane1551]

For example: 230/10ohms Vs 250/10 ohms... Which gives you the most current?

[@scwfan08]

9000 is the power in watts. not the resistance

[@deang5622]

"Electrician's Guide"? Seriously? Surely qualifued electricians studied this in their City and Guilds courses?