Cross normalling is slightly more descriptive to an operator than double innered which is the (BBC) engineering term. But it is an ITV term. And you tend to refer to plugging up a jackfield rather than jacking it up which sounds slightly rude.
But "double innered" is not the same a "normalled", I can see that is slightly simpler to understand though. Double innering needs two plugs to be inserted to isolate the source and destination, you need to "jack out" the unwanted inner.
Normalling is broken with just one plug.
Gawd this is ancient stuff I had to draw it out, don't often see double innered stuff these days or listen/source/destination (or something like that). These days why use 2 or 3 sockets when one will do...
B-) Plugging up yes, but you "jack out" double innering.
Cross normalled is the same as double innered - ie two jacks which are both listens until both are used when they both become break jacks. At one time, you'd have a two listens and two breaks. With cross normalled, it allows you to isolate both source and destination with two less jacks for almost all applications.
Yup.
Still in use, though. Not everything is digital.
Either would do.
At this point I just give up. The words "horse", "dead" and "flogging" come to mind.
Wrong. 2.5mm^2 will usually be fine for the socket runs. Overload protection is provided by the plug-top fuses, s/c fault protection by the fuse or MCB in the consumer unit. Strictly speaking the designer should check that disconnection time and cable thermal protection requirements are met, but, with MCB protection and normal circuit lengths of a few metres from the split, there won't be a problem. This combination of device rating and cable size is no different to that of the unfused spur taken from a 32 A ring circuit.
In fact 1.5mm^2 would probably be OK for the socket runs in most cases, but would certainly need to be checked by calculation. Sticking to the conventional 2.5mm^2 gives a degree of belt'n'braces safety.
I know how you feel. The regs are at time very non-specific.
And if the overload is pre the plug?
True enough, just doesn't "feel" right. Like I said I haven't thought that hard about the practical requirements of installation only the I want this feature.
That can't happen - the branch is feeding one socket only. (Unless you connect three 3 kW fires through an ancient unfused 3-way adaptor...)
Consider the fact that for all sizes of T&E cable except 1.0 mm^2, the earth conductor can be 'undersized' relative to the fuse rating. This is OK and it is known, by design, that in the event of an earth fault the fuse will blow before the earth wire in the cable overheats. The situation is the same with an 'undersized cable' where overload protection is either not required, or is provided downstream.
It's important to distinguish between 'faults' - i.e short-circuits caused by someone cutting through a cable, or whatever - and 'overloads' where the design load is exceeded - too much equipment connected, relative to the design expectations.
Fault and earth fault protection is always required. Overload protection is required in general, but can be omitted where the characteristics of the load are such that overloading just can't happen. For example, a circuit feeding a single heating appliance is designed for the maximum loading of the appliance and doesn't need overload protection. Overload protection can also be separate from the fault protection and can be downstream, as in this case. The industrial motor circuit is another common example. The fuses in the dis-board only provide fault protection for the wiring; overload protection comes from an 'overload relay' in the motor starter.
Does that mean when the dishwasher has to be sent back for repair, you can't use the washing machine because you can't turn off the hose individually?
Christian.
Can you get washing machine conectors without a valve built in? I was really thinking of taps etc...
In any case, the same point still stands. You may wish to isolate one outlet until the opportunity arises to complete a repair. If you have a badly leaking tap that requires a 'O' ring to be ordered in, would you want the entire kitchen isolated until you can get round to ordering and fitting it?
As isolating valves cost 49p at screwfix and take seconds to fix, why not bother installing them?
Christian.
15mm x 3/4" BSP male, BES 9011
should be it
.andy
To email, substitute .nospam with .gl
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.