60A Fuse box - is (typical) over 60A max load OK?

[Msitekkie]

This relates to one of those old 60A Wylex Fuse boxes that has been upgraded with MCBs - I know it would be a very good idea to upgrade, but the question is, how does the "Max 60A" rating moulded on the box apply? The main fuse is 60A and the load after diversity calcs is 89A.
I am aware that this is not an unusual load for a typical house with a 60A main fuse (which can safely maintain higher loads for a relatively long period as per the time/current graph), but less clear how it applies to the fuse box & whether a 60A Fuse box was typically intended to be paired with loads suitable for a 60A main fuse. Is this limit in fact a further limiting factor on the overall load, due to things like temperature limits on the components in the fuse box, or maybe how well the main switch can cope with arcing (if say somebody tried to throw it at full load).
i.e. Diversity figures should be strictly applied in this scenario (in spite of that making the box unsuitable for most typical homes)?

 

[davesparks]

89A for a house? Are they growing weed in there?

 

[jackhammerJIM]

how many circuits and what are the circuit ratings ?
There must be a lot for you to get 89 amps after diversity

 

[Baddegg]

89A after! Can’t be more than 6-8 ways on the board surely? What was ya total before diversity?

 

[bill01803]

Are you saying it is a 60A main switch, I have only ever seen one melted one in 3o years.

 

[Wilko]

Hi - I think The Book answer is the board was certified as safe for 60A load. The main fuse is there to protect the supply cable and should not be relied upon to protect the board. Practically speaking, with 60A fuse and sensible domestic loads it will probably outlast us all.

 

[Msitekkie]

To try & respond to some of the replies:
There are 7 circuits +1 spare
Upstairs + Downstairs lights & sockets =4
Kitchen ring
Immersion Radial
Cooker Radial
Main loads are 20A cooker, 31.3A hob, 13A Immersion heater
For practical diversity calcs I treated the kitchen ring as part of the downstairs ring.
So not really unusual at all.
I have no specific rating for the main switch, the 60A Max rating is moulded along the bottom in the plastic, so I think applies to the unit as a whole.
I accept the point made about the main fuse, but it's not directly relevant to the question.
I don't think anybody really answered the question except possibly Wilko, although the question really was, what does that 60A certification mean in practice (e.g. overheating) and given that 60A fuses were typical when these boards were sold, was there likely any co-relation that the manufacturer intended these boards to service loads that would be typical with such a fuse & I make the contention that this is a fairly typical load.
Presumably also Wylex would have allowed some margin.

 

[westward10]

That switch complied to BS5419, superseded by EN60947-3. These standards require/required a switch to carry its rated current and be able to be switched whilst carrying this current. The standards also allow for overcurrent but not necessarily short circuit or fault current.

 

[dmxtothemax]

QUOTE - Presumably also Wylex would have allowed some margin.

For sure !

Typically the margin is 100%
So if the cu is rated for 60A ?
in reality it can cope with up to 120A
So 60A Is really it's safe working load,
And not it's actual maximum load.
"fudge factor"

 

[Lucien Nunes]

20A cooker, 31.3A hob

So 51A / nearly 12kW total for cooking? Doesnt sound like the diversity has been correctly applied. The cook would probably succumb to heat exhaustion before anything happened to the main switch.

The switch is rated for 60A and therefore should be safe for any load that close OCPD with In=60A can pass through it. One should not design for Ib>In therefore the switch should never normally see >60A, but if it does, it will not immediately burst into flames.

It takes concerted effort to use >60A in a normal family home without an electric shower.

 

[davesparks]

So 51A / nearly 12kW total for cooking? Doesnt sound like the diversity has been correctly applied. The cook would probably succumb to heat exhaustion before anything happened to the main switch.

We are gathered here today to witness the final passing of Christmas Dinner, the cremation of its earthly remains........