Simple plug question

[plugwash]

Why would you fit a 5a fuse when one of the connectors is only rated to 2.5a?

Many items have an inrush current when first turned on that is much higher than the normal running current, the exact mechanism for this varies between types of device, for devices with mains powered motors the inrush current comes from the fact a stalled motor draws far more current than a running motor. For electronics the inrush current comes from charging the primary capacitors. This inrush current is normally too short in duration to post a threat to the cable, but it can sometimes blow fuses that are sized to match the nominal rating of the cable, either immediately or later through thermal cycling of the fusewire slowly weakening it.

Fuses for use inside equipment come in multiple different "blow characteristics", as do the MCBs used in electrical distribution boards, so a fuse/breaker can be selected to match the inrush characteristics of the load. However plug fuses only come in one type, so if you are having problems with fuses blowing due to high inrush current your only real option is to increase the current rating.

It's worth noting though that what Sony consider a problem and what you might consider a problem are not one and the same. For high volume low-margin consumer products returns are a major cost center and companies will work to drive them down to almost insanely low levels. Fuses like any component have tolerances and generally quite wide ones, if the inrush current blows say the weakest 1% of 3A fuses after a year than that is likely to be regarded as a big problem by Sony whereas for most of us it would be "meh".

Isn't that a risk in itself?

Not significantly, the PS5 like most modern consumer electronics is sold across the world and the vast majority of countries don't use fused plugs, so faults in the device itself that may cause an overload but not a sufficient overload to trip the breaker need to be dealt with inside the device.

 

[JohnW2]

.... However plug fuses only come in one type, so if you are having problems with fuses blowing due to high inrush current your only real option is to increase the current rating. ...

That's what I (and probably nearly everyone else) would have said, but are things like these 'for real', I wonder (no mention of BS1362 that I can see)? ...

Kind Regards, John

 

[plugwash]

I'm sure there are plenty of non-standard fuses that would physically fit in a BS1363 plug. I'm also pretty sure that no sane reputable manufacturer would even consider fitting such a thing,

 

[JohnW2]

I'm sure there are plenty of non-standard fuses that would physically fit in a BS1363 plug.

Indeed - like the 15A and 20A ones

I'm also pretty sure that no sane reputable manufacturer would even consider fitting such a thing,

I would hope that is probably true. However, it's perhaps a pity that the Standard does not (well, I presume not!) include slow-blow fuses, since that would sometimes avoid the need to use a fuse of 'otherwise unnecessarily high' rating in situations such as you mentioned (when there are very brief 'inrush' currents).

Kind Regards, John

 

[securespark]

Mains leads using 0,75mm² flex are routinely fitted with 13A fuses in the factory, which I think is wrong, as the rating of that size flex in the regs is 5A. If a C7/8 connector is rated at 2.5A, I feel it should be supplied by a 2A fuse.

 

[bernardgreen]

Note the different names,

 

[JohnW2]

Note the different names,

I don't think we would have expected otherwise, would we?

Kind Regards, John

 

[plugwash]

Mains leads using 0,75mm² flex are routinely fitted with 13A fuses in the factory.

Meanwhile mains leads are also made with un-fused Australian plugs. I'm not familiar with australian wiring regulations as to what sockets can be fitted on what circuits, but given that their 32A sockets will accept regular 10A plugs it seems like a mains lead could very easilly end up only protected by a 32A breaker.

The Australian IEC leads that farnell sell do appear to be 1.0mm² rather than 0.75mm² flex though.

BS1363 implies (though doesn't explicitly state) that a 13A fuse is acceptable for any flex of 0.75mm² or larger, indeed IIRC for years 3A and 13A were the only common sizes of BS1362 fuse, 5A became common later.

What i've never seen anywhere is a standard that states what leads/adapters are or are not acceptable to make/sell. There are standards for installations, both permanent and temporary, but a lead is not an installation. There are standards for connectors, but at least the ones i've read typically say very little about how those connectors should or should not be used.

The current reality seems to be that it's up to the user to ensure that pluggable leads are adequarely protected (for whatever values of adquarely) and/or not overloaded.

 

[JohnW2]

BS1363 implies (though doesn't explicitly state) that a 13A fuse is acceptable for any flex of 0.75mm² or larger....

I'm not sure what you mean by "doesn't explicitly state". Agreed, it does not apply "for any flex of 0.75mm² or larger". However, per Note (c) of the table below, BS1363-1 appears to indicate that 0.75mm² or 1.0mm² flex is allowed with a 13A fuse if it is part of a "cable set with a non-rewirable plug", provided that the cable is no greater than 2m in length....

Kind Regards, John

 

[plugwash]

Either I missed the "normal use" bit in the title of that table and thought it was only for tests, or it changed between editions.

 

[JohnW2]

Either I missed the "normal use" bit in the title of that table and thought it was only for tests, or it changed between editions.

Fair enough. That comes from the 2016 version, which I think is still "current".

Kind Regards, John