MEM TP&N Switched Fuse Question

[uksparks]

Hi,

I have a 32A TP&N MEM Switched Fuse, I really could do with a 63A.

Question, can you just change the fuses? Or do I need to buy a whole new unit?

If need a new one, is anyone selling one?

Also, I have 10mm tails into the 32A unit, can I get 16mm into the 63A does anyone know?

Cheers.

 

[Guest112]

the unit itself will be rated at 32A so I wouldn't , and yes 16mm tails will fly into a 63A unit

 

[uksparks]

Thought as much, anyone got one for sale then?

 

[davesparks]

Something go pop when you turned it on then?

You'll need to get a new one I'm afraid, you can't just up the fuses!

You'll be looking for a 60kxtnc2f if you are going for MEM,

You can get cheaper alternatives, I've fitted a square D twinbreak unit in the past. It was ok but not quite as good as MEM in my opinion.

If I remember correctly the MEM one will take up to 35mm cables, you may find 16mm is a bit 'dick in a bucket'

 

[davesparks]

Thinking about your installation (assuming it's the one from the other threads) I don't see the need for a switchfuse.
It would be cheaper to get a bigger enclosure to house a TP mcb, coil cct mcb and the contactor. And a bit of trunking to tidy it all up!

 

[Knobhead]

As I recall the MEM switches use TIA fuses.
You can get TIS 45 & 63 with the same barrel size but the lugs are slightly wider. Length is the same so a bit of work with a file.....
Your call, I’m not saying yea or nay.

 

[ipf]

This is a no brainer....if you need a 63amp, fork out for it.

 

[uksparks]

Hi,

I have found a MEM 63A switch fuse on eBay, just snapped it up for £60 delivered, unused, well it was installed but nothing connected he said, looks new

The issue I have is that I have 12 storage heaters that are going to be drawing about 98A across three phases, the old ones were less powerful.

thing has blown, but I need to rejig for the following reason.

i have balanced the board out so that on phase one, I have 44A or heaters, same again on phase 2, and on phase 3 I have 10A. I now hear you saying that's not balanced... Well.. So this is why I need a 63A switch.

The 24 hour board is connected to phase 3 but on another meter, that board, I now have a sodding dilemma as there was never a power shower previously.

third phase loading:

Heating on other board 10A

Shower 45A
hob 30A max
cooker inc socket 22A max
lights 0.7A
security lights 1.8A
plugs inc kitchen say 20A max peak

Now, you see I want to fit a 32A car charger as I can get £1000 back for helping out £375, but now think I hve no damn capacity for it.

i am a bit maxed out aren't I!

 

[uksparks]

Oh by the way, I fitted a 6A breaker next to the Contactor and it works a treat, now I am going to change the tails and switch fuse and take it part gain, I'll sap the plastic enclosure with the Contactor for a metal one.

 

[uksparks]

Thinking about your installation (assuming it's the one from the other threads) I don't see the need for a switchfuse.
It would be cheaper to get a bigger enclosure to house a TP mcb, coil cct mcb and the contactor. And a bit of trunking to tidy it all up!

You see I thought do away with it then I thought, no because it could be overloaded, then I thought, I could just stick a TP 63A mcb in an enclosure, hang about you have just given me an idea...

could I then, get an enclosure, put a TP 63A MCB in it, fed from the isolator, then that feeds the top of the Contactor, then the Contactor to the board. The 6A mcb in there as well for the control circuit. That would work wouldn't it? Damn that's a better idea.

 

[uksparks]

What about putting 3x 63A SP mcbs in as you would only lose the overloaded phases in the event of an overload. Just a thought.

 

[davesparks]

Maxed out? that's nowhere near it!

What is the power rating of the shower?
How did you get to a combined total of 52A cooker load?

 

[davesparks]

If I had been doing this install from scratch I would probably have fitted a contactor incomer to the TPN board (you've got an external DNO supplied main switch there). And found a way to avoid putting the storage heaters on an RCD, assuming the RCD is only there for the buried cables bit it's easy to avoid.

 

[uksparks]

Shower is 10.8kW, no diversity allowed...

The hob is new, uses 7kW max, so took 10A plus 30% say 18A - 20A

Cooker control unit plug, 5A plus 10A for cooker plus 30%, cooker uses 18kW, so 15A plus 7A say, 22A ish max potential,
ok

45A for cooker and Hob, 45A for shower which will draw that as its the sme as mine and that does when on full. So there's 90A plus the 10A for storage heaters on that phase which boost mid afternoon.

 

[uksparks]

If I had been doing this install from scratch I would probably have fitted a contactor incomer to the TPN board (you've got an external DNO supplied main switch there). And found a way to avoid putting the storage heaters on an RCD, assuming the RCD is only there for the buried cables bit it's easy to avoid.

Solid brick walls down stairs and some up and it would have been a non starter burying cables 50mm in wall, I did think about it, plus it's going to be rented out so rcd is a good idea just to be safe.

i think I'll either get an enclosure and redo the bits, or stick with this new switch fuse now bought it and stick a new metal clad box in for the Contactor.

 

[uksparks]

Helping out, I mean shelling out £375.#8

 

[davesparks]

Solid brick walls down stairs and some up and it would have been a non starter burying cables 50mm in wall, I did think about it, plus it's going to be rented out so rcd is a good idea just to be safe.

i think I'll either get an enclosure and redo the bits, or stick with this new switch fuse now bought it and stick a new metal clad box in for the Contactor.

No need to go 50mm deep, use steel conduit in the chases and the job's a goodun.

How would the RCD make the heaters any safer in a rented property? Seriously, RCDs seem to be treated like this magic device which makes electricity safe and excuses poor installation work (not suggesting your work is poor but a generalisation)

 

[uksparks]

It does help though when some numpty drills a hole and hits your cable. Oh the famous 1667 ohms and all that, I just feel as its going to be rented it does add a degree of protection for the end user who doesn't observe safer zones.

 

[davesparks]

Shower is 10.8kW, no diversity allowed...

The hob is new, uses 7kW max, so took 10A plus 30% say 18A - 20A

Cooker control unit plug, 5A plus 10A for cooker plus 30%, cooker uses 18kW, so 15A plus 7A say, 22A ish max potential,
ok

45A for cooker and Hob, 45A for shower which will draw that as its the sme as mine and that does when on full. So there's 90A plus the 10A for storage heaters on that phase which boost mid afternoon.

I'd suggest revisiting your diversity calculations.

I quote "First 10 amperes + 30% f.l. of cooking appliances in excess of 10 amperes + 5 amperes if socket outlet incorporated in control unit"

So you have a max cooker load of 18KW + 7KW = 25KW
assuming these are 240V ratings as they usually are (funny how they never changed appliance ratings to suit the supposed voltage change and just added the lower 230V ratings into the specs)
25000/240 = 104A
minus first 10A = 94A
30% of 90A = 27A

So 10A + 27A + 5A (socket) = 42A

Shower of 10.5KW = 43.75A

= total 85.75A

Add to that the chances of anyone being home and cooking and showering at the same time at 15:00 (afternoon boost time)?

Don't forget diversity applies to you heating load too so:
Max heating load 96A
minus first 10A = 86A
50% of 86A = 43A

So 10A + 43A = 53A

Balance that across the phases and you get 17.66A / phase

All in all someone is going to have to be cooking and having a shower and got the washing machine running and a few other appliances drawing and the lights on when the afternoon boosts kicks in to create a big enough overload to blow a cutout fuse of the overload is sustained for a good few hours.

 

[davesparks]

It does help though when some numpty drills a hole and hits your cable. Oh the famous 1667 ohms and all that, I just feel as its going to be rented it does add a degree of protection for the end user who doesn't observe safer zones.

If its rented they won't be drilling into the walls.

If they drill into the steel conduit with a DIY hammer drill they will vibrate the steel conduit enough for all the plaster to fall off before they get through it.

Storage heaters will give you some lovely calbacks to deal with nuisance tripping when they first get turned on after summer.

 

[uksparks]

Thanks for that, I guess I was taking it a bit too literally maybe, the heating isn't too bigger issue as on other phases.

I reckon it will be fine to stock a 32A charger for a car in too, pushing the boat out a bit, but there's over £500 in it for a quick bit of work.

 

[uksparks]

If its rented they won't be drilling into the walls.

If they drill into the steel conduit with a DIY hammer drill they will vibrate the steel conduit enough for all the plaster to fall off before they get through it.

Storage heaters will give you some lovely calbacks to deal with nuisance tripping when they first get turned on after summer.

They should not be drilling, we shall see what happens.

The storage heaters are all brand new so hopefully should have many issues.

Ill post up a load of pics on here of the completed project when done in a couple of weeks so you can see, it wasa big one for me on my own to do.

Anyway, I'm going to sleep now, thanks for the chat!

 

[davesparks]

I've got a commercial building I do maintainance at with standard 100A TPN supply.

Total connected load after diversity (lots of aircon) works out around 120A per phase (assuming balanced)
Actual load recorded on a load study (middle of winter, snow on the ground)
L1 peaks at ~120A
L2 peaks at ~60A
L3 peaks at ~40A

The DNO come out and change the cutout fuse in L1 at approx 18month intervals, it has only happened once since I took over the maintenance and that is what prompted the load study.

The job is in planning for all new switchgear and balancing of the loads, was set to go ahead but all of the aircon kit got written off when the river rose and flooded it all this winter. So a complete new aircon system requires completely different supplies.