15A through a 13A plug

[5010m0n]

Hi All

Just to start off, my understanding of electric wizardry is reasonable but basic.

I have a brewery that I am upgrading in size and power. Here's the rough electrical plan... forgive me if I use the wrong terminology.

• Starting at the fuse board, there's a 30A fuse.

• Then a 30A rated cable supplying power to my control centre.

• Amongst the other gubbins I've got on the control centre I've got two fused spur switches (13A). Each of these switches controls remotely, via 30A rated cables, a socket outlet (one outlet per switch... I've chosen this layout because switches on my control centre are more easily accessible than the socket outlets themselves - the outlets remain switched on at all times and their power is controlled by the switches on the control centre).

• My elements, which are 2.75kW each are then plugged into the socket outlets using standard domestic 13A fuses.

By my reckoning my current setup draws around 23A (about 11.5A per element) and this system has proved to be stable and robust.

Now I would like to upgrade my elements to 3.5kW each. Again, my reckoning says that the 30A parts of my setup will handle this fine because the max current being drawn at any one time will be a smidge over 29A... however each individual element will pull 14.6A which exceeds the 13A rating of both the socket outlet and the fused spur switches.

My first question (or series of questions... will this simply not work? will the fuse blow immediately or is there a built in tolerance?

My second questions... if this will not work, what are my options?

Thanks!

 

[JohnW2]

Amongst the other gubbins I've got on the control centre I've got two fused spur switches (13A). Each of these switches controls remotely, via 30A rated cables, a socket outlet (one outlet per switch... I've chosen this layout because switches on my control centre are more easily accessible than the socket outlets themselves - the outlets remain switched on at all times and their power is controlled by the switches on the control centre). ... My elements, which are 2.75kW each are then plugged into the socket outlets using standard domestic 13A fuses.

To have the 'remote' switches for convenience is fair enough. However, there is no need for them to be 'fused spur switches', since there is already a 13A fuse in the plug - an adequately rated switch (without fuse) would have been satisfactory.

Now I would like to upgrade my elements to 3.5kW each. ... each individual element will pull 14.6A which exceeds the 13A rating of both the socket outlet and the fused spur switches. My first question (or series of questions... will this simply not work? will the fuse blow immediately or is there a built in tolerance?

A 13A fuse will not blow for a long time, if ever, with 13A flowing. However, you should not do it. Not only is it contrary to regulations but, apart from anything else, even with 13A flowing, 13A plugs can get quite hot, sometimes even burning.

My second questions... if this will not work, what are my options?

You should not attempt to supply a 14.6A load through either a (13A) FCU or a 13A plug/socket. It really depends upon whether the elements require independent fusing (the manufacturers may say that they do), If not, you could simply 'hard wire' both the elements to the circuit (converting the present sockets to some sort of 'connection unit', maybe like the ones used for cookers), using just an appropriate switch (no fuse) in the feed to each of them. If there is a requirement to have separate fuses (or MCBs) for each element, then things would get a bit more complicated.

I’m a little surprised that you see the need to upgrade from 2.75 kW to 3.5 kW elements (hence invoking these various issues/problems). What is the reason?

Is this a domestic 'brewery' or a commercial one?

Kind Regards, John

 

[ericmark]

A 13A fuse will take a long time to blow at 14A if it ever blows but all fuses give out heat that is how they work and the fuse carrier has to dissipate that heat or the carrier will over heat. The 13A plug is a fuse carrier and it needs to be in free air to cool.

With for example a domestic kettle the current is only drawn for 5 minutes so there is time for the plug to cool before the next time it is used.

Move to a 5 gallon tea urn and we are looking at half an hour to boil so the plug will get much hotter. As we then look at an immersion heater then the 2 to 3 hours from cold to the thermostat starting to work could very likely cause the plug to over heat.

As a result it is recommended any fixed appliance over 2kW has a dedicated supply and with items like an immersion heater we if plugged in would use a 15A plug with no fuse in it and use a 16A MCB to protect for over current.

The fused connection unit (FCU) can get rid of the heat far better than a plug so using a FCU and a 15A socket would likely remove the over heating problem. However once you look at that then using a sub consumer unit with 16A MCB's would likely cost less and be a much neater job.

Also with so much liquid involved RCD protection must be considered and although you can use surface wiring and RCD FCU to each 15A socket using a single RCD and MCB's in a sub-consumer unit would be far cheaper.

With the kettle in the main it is monitored and any discolouring showing the plug has over heated will be noticed. With a large urn type unit it is likely the plug will not be removed very often and the degrading could result in when you try to remove the plug live parts will be left behind in the socket.

When I got a new induction cooker I was impressed with the 3.75kW heat area of the hob. But when I came to use it I found with the exception of plain water the heat was far too much and food just burnt onto the bottom of the pan. At 1.85kW it did take a pan of cider juice (6 pints) 20 minutes or so to boil and it is tempting to use the 3.75KW option but once one has tried to clean the pan after one realises better to take a little longer and be able to simply swill out the pan.

Much depends on the area in contact with the liquid of course but unlikely any element will have an area greater than the bottom of my pan. Although Simmer stats can reduce the power they tend to have a large on and off time and during the on time do tend to allow stuff to burn unless there is a very large heat sink to damp down the switching effect. This is the whole idea of copper bottom pans which will not work with my cooker.

As a brewer I am sure you understand speed is not always good. Hence the brewing using lagering process.

 

[5010m0n]

Thanks for your considered responses, guys. There's a lot for me to take in here.

The reason for my upgrade is my plan for continued growth to go commercial. I am moving from 60l barrels to 200l and beginning to sell wholesale and retail. In terms of commercial scales, this could be considered to be a nano or even pico brewery... It doesn't get much smaller. The increase in power will just speed the brew day up a bit. My next size upgrade will be to dedicated premises (and not just the back of my garage) and to call in the experts.

The elements I am looking at will be imported from the USA (although they are rated at 240V) and are ultra low watt density so the possibility of them actually burning the wort as it is boiling is removed.

To make beer the wort needs to have a good rolling boil for at least an hour... Heat build up in the plugs could be an issue.

How about replacing my fused switches with something more substantial, like those cooker spur switches, and replacing my socket outlets with 30A junction boxes? Would that be a solution? Or is that a solution you have described already only put in layman terms?

 

[JohnW2]

The increase in power will just speed the brew day up a bit. ...To make beer the wort needs to have a good rolling boil for at least an hour.

Yes, I assumed that from what you said, but I was really questioning whether an increase of less than 30% was going to make much difference - had you proposed to double or treble the power, I could have understood more! I presume it's only a question of how long it takes to get to boiling temperature - I presume that, once it is boiling, it will take relatively little power to maintain that boil.

The elements I am looking at will be imported from the USA (although they are rated at 240V) and are ultra low watt density so the possibility of them actually burning the wort as it is boiling is removed.

Fair enough - but be careful! We have a constant flow of questions here from people who have bought equipment from US which are said to be OK for use on a UK power supply, but which prove to have problems when they arrive!

How about replacing my fused switches with something more substantial, like those cooker spur switches, and replacing my socket outlets with 30A junction boxes? Would that be a solution? Or is that a solution you have described already only put in layman terms?

That is, indeed, essentially a re-wording of what I was suggesting - as I said, rather than junction boxes, you could probably use 'cooker outlet plates', more-or-less designed for the job. However, as I said, that approach is only acceptable if there is not a requirement for the elements to have individual fuses/MCBs - do you know whether the manufacturer of the proposed elements makes any stipulation about this? As eric has said, if there were a requirement for separate protection (fuse/MCB) of each element, then the simplest solution would probably to have two 16A MCBs in a small enclosure.

Kind Regards, John

 

[OwainDIYer]

With your loads, 13A plugs and fuses are best forgotten.

You can get commercial immersion heater elements in the UK - up to 9 kW single phase

http://www.backerelectric.com/products/industrial_immersion_heater.asp

http://www.milkingmachines.co.uk/uk2shop-11.htm

You need to consider overheat protection as most immersion heater thermostats won't handle more than 3 kW and also the UK usually requires secondary over-heat cutout protection.

You could take the 30A cable to close to the element location(s) then have a local distrubution unit with individual RCBO protection for each element and a contactor for remote control. Then you'd only need to run low-current wires from the contactor coils back to your control location.