Omission of overload protection for fixed loads.

[Silly Sausage]

Oh deary me, what appeared at first to be a serious discussion, with self proclaimed superior engineers, then falls apart mid thread with an elementary electrical theory error...and all the abuse 5WWs get!

You've got to laugh!!!! :ciappa::smilielol5::smilielol5::smilielol5:

 

[Darkwood]

Outspoken ... just to relay a answer to your reply regarding back tracking i read my first post as stating the regs do permit it on a water heater but i also state that i dont believe it should be applied in a domestic environment when in commercial or industrial the environment is usually more controlled and likely to remain as installed, if your playing the voltage change card this could apply to any circuit calculation you make where you enter 230v as nominal voltage, the regulations have tolerances on the caution built in to the tables to allow for these things, we are told to calculate to 230v but im 99% of the time seeing voltage in the mid 230s to mid 240s yet we still use 230v when designing a circuit.

 

[Darkwood]

This is a really good debate, Darkwood has bought up a really good point that I've honestly never thought of in a domestic situation.

Personally I don't think anybody should be using this reg in domestic situations. A shower is a fixed load, same as a water immersion. But along could come Jo blogs and add this on add that on and than a fixed load is a lot larger.

I though will be using this reg to my advantage.
in the airport where I work we see a lot of lighting MCBs tripping out when contactors click over. These circuits serve fixed display stands in shops that never change and nor do the install conditions apsurrounding it.
Where nuisance tripping had occurred on the inrush of florescent tubes even on D16 breakers we than can look at upgrading the breaker to D20/32.

What would happen to your permitted Zs its this that usually limits you from doing this, you still have to meet requirements in the event of a short circuit.
You shouldn't be applying this really because you have designed the circuit wrong and put more fittings than the mcb manufacturers guidance notes, the discussed regulation should only be applied when its impractical to have the mcb lower than the ccc of the cable in which as an example is a motor circuit where trying to keep the mcb high enough to allow for inrush yet ensuring the cable isn't 2 -4 times larger than necessary for the fLC of the motor which has its own O/L protection anyway.

 

[44ALLAN]

He's comatose :rolleyes2::54:

 

[SimpleSimon]

What would happen to your permitted Zs its this that usually limits you from doing this, you still have to meet requirements in the event of a short circuit.

It's exactly as you put it, my Zs would limit me. I could move it from a 16 to a 20 but a you say unless it was 4mm I'd be kinda stuck there, usually these are 4mm because of the volt drop and 16 because of the small load.

 

[spark 68]

Another Possible limitation is if there are any B15,B22,E14,E27 and E40 fittings anywhere on the circuit, as the max OCPD for any of these is 16A.

 

[Darkwood]

It's exactly as you put it, my Zs would limit me. I could move it from a 16 to a 20 but a you say unless it was 4mm I'd be kinda stuck there, usually these are 4mm because of the volt drop and 16 because of the small load.

I edited my last response to you, you be good to get technical tables from your mcb manufacturers as these state the amount of different types of lamps you can have on a given mcb and this is what you have fallen foul off here.

 

[SimpleSimon]

Another Possible limitation is if there are any B15,B22,E14,E27 and E40 fittings anywhere on the circuit, as the max OCPD for any of these is 16A.

Good point, but they are usually LED drivers and tape and fluorescent fittings.

 

[SimpleSimon]

I edited my last response to you, you be good to get technical tables from your mcb manufacturers as these state the amount of different types of lamps you can have on a given mcb and this is what you have fallen foul off here.

Would these include fluorescent fittings and LEDs?

 

[Outspoken]

Oh deary me, what appeared at first to be a serious discussion, with self proclaimed superior engineers, then falls apart mid thread with an elementary electrical theory error...and all the abuse 5WWs get!

You've got to laugh!!!! :ciappa::smilielol5::smilielol5::smilielol5:

Now that is misreading reality if ever there was a case of it Archy, but glad you had a laugh at my expense..

 

[Outspoken]

He's comatose :rolleyes2::54:

No, just had some food and several cups of coffee to mitigate the impact of the wine.. :8:

 

[Outspoken]

Outspoken ... just to relay a answer to your reply regarding back tracking i read my first post as stating the regs do permit it on a water heater but i also state that i dont believe it should be applied in a domestic environment when in commercial or industrial the environment is usually more controlled and likely to remain as installed, if your playing the voltage change card this could apply to any circuit calculation you make where you enter 230v as nominal voltage, the regulations have tolerances on the caution built in to the tables to allow for these things, we are told to calculate to 230v but im 99% of the time seeing voltage in the mid 230s to mid 240s yet we still use 230v when designing a circuit.

Thank you DW, that clarifies your position far better than your earlier posts did, but then I do have to question the motive for the OP and your statement at the end ofit because the two positions you have seem at counterpoint to each other.

 

[Richard Burns]

I felt the original post was a well reasoned statement that indicated the difference between:
applying the regulations to all situations no matter the circumstances
and
considering the design of your installation and applying the regulations with consideration for safety.


Since BS7671 is the minimum standard to apply, ensuring that you install overcurrent protection to a cable would be a good thing in the main, even if there is a regulation that potentially allows a "get out clause".

 

[somersetsparks]

I felt the original post was a well reasoned statement that indicated the difference between:
applying the regulations to all situations no matter the circumstances
and
considering the design of your installation and applying the regulations with consideration for safety.


Since BS7671 is the minimum standard to apply, ensuring that you install overcurrent protection to a cable would be a good thing in the main, even if there is a regulation that potentially allows a "get out clause".

'get out clause' Sums it up nicely for me
It suggests that "it's not right but it's okay" if it's already like it.
which I think is certainly the case with an existing 6mm shower circuit supplying an 8.5 shower

 

[Engineer54]

Well i've just read through the whole of this thread, and basically we are now down to just splitting hairs. For me, and for all practical reasons i'll stick to the long standing view that a circuit supplying a fixed load can't produce an overload condition of any consequence!! Now whether you want to include DIY Dave, or anyone else into the equation by adding spurs, tap offs or whatever in to that circuit, that's a whole new ball game... lol!!