What size Fuses do I require?

[Gavin Millar]

Hi,

I have a three phase switch fuse supplying a 16A socket. In the specification provided it states the following:

Design Current - 16A
Main Protective Device 20A

The circuit is fed from a C20 MCCB at the distribution board.

What size of fuses should I be putting in the switch fuse?

16A or 20A?

Thank you.

 

[westward10]

What wouldn't achieve discrimination with the 20A device.

 

[GMES]

Perhaps some discussions among staff members would be a good idea, all on the same page so to speak.

Staff do discuss things and I know exactly what you're referring to, which proves we do.
My only point is that we are getting reports by members that it is becoming almost a stock question.
As for incomplete profiles even if was compulsory it would not guarantee that new members would fill them in truthfully.
All we're asking is for you and others to evaluate the question from any given op and answer that question, it can almost put the op or thread on the back foot before it's begun.
That's all we are asking , nothing more nothing less.

 

[Octopus]

Yeah we are getting a fair few reports about the constant questioning of quals and empty profiles, maybe we could just start answering the questions with a relevant answer.
Cheers
GMES

Not sure I agree with that.

New members do not open up their profiles so we are all guessing ................

This is not a DIY superstore site...........

 

[Squid]

great thoughts pete,but please translate them from latin for the younger members. .

Stone slabs are hard to scan Tel....... as they scratch the glass......

 

[Squid]

Are certs still valid for old farts......?

 

[GMES]

Not sure I agree with that.

New members do not open up their profiles so we are all guessing ................

This is not a DIY superstore site...........

If you don't feel comfortable answering then don't answer, we would never expect anyone to answer something they're not comfortable with.
I also know it's not a diy superstore and the op isn't a bank holiday shopper , he's a trainee on a proper college course.

 

[telectrix]

What wouldn't achieve discrimination with the 20A device.

16 A fuses may not achieve discrimination with a 20A MCCB, IMO.

 

[westward10]

16 A fuses may not achieve discrimination with a 20A MCCB, IMO.

Got you Tel just reread #1.

 

[Octopus]

If you don't feel comfortable answering then don't answer, we would never expect anyone to answer something they're not comfortable with.
I also know it's not a diy superstore and the op isn't a bank holiday shopper , he's a trainee on a proper college course.

Then he should be enrolled in the training section .................. like many others .................

 

[GMES]

Then he should be enrolled in the training section .................. like many others .................

See #11

 

[westward10]

Then he should be enrolled in the training section .................. like many others .................

When his thread was approved it was not clear that he was a trainee, a later post indicated he was so I believe things are in motion to put this in place.

 

[Flanders]

To the OP I believe if you look in GN1 it gives a suggested maximum overcurrent protective device of 20A. I believe this is due to the fact a radial of more than one 16A socket can be employed, after this 32A, 63A etc... are suggested to be single point radials with a 8protective device used to match their rating. If however the circuit supplies one 16A socket I see no reason to use anything above a 16A protective device.

If you protected two 16 amp sockets with a 20amp mcb whats is to stop one of the sockets being overloaded ? as 16 amp plugs do not come with fuses in them , or have i miss understood?

 

[westward10]

If you protected two 16 amp sockets with a 20amp mcb whats is to stop one of the sockets being overloaded ? as 16 amp plugs do not come with fuses in them , or have i miss understood?

Although not quoted in BS7671 I believe this is what GN1 states, not real it for a good while though.

 

[Flanders]

Although not quoted in BS7671 I believe this is what GN1 states, not real it for a good while though.

I would have to disagree with GN1 then , as designing the circuit this way you could plug a 20 amp load into the 16 amp socket , now to be fare the 16amp socket could probably take the extra 4 amps , but they are not designed for this and over time would overheat.

 

[Octopus]

Discrimation aside a 16A socket should be protected by a 16A OCPD