what is max current for this cable please

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Hi there,

got some "SWA BS5467 2 x 1.5mmsq" whats the max current rating assuming its mains voltage please?
 
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It depends on the length of the run, the ambient temperature of the run, wether it is grouped with other cables, wether it runs in thermally insulating material, and what type of overcurrent protective device it is connected to.
 
A ball park figure would do me but:

It depends on the length of the run, -- 50M
the ambient temperature of the run -- UK garden
, wether it is grouped with other cables -- NO
, wether it runs in thermally insulating material - lying on the ground / might bury one day

, and what type of overcurrent protective device it is connected to. -- This is partly what im trying to determine. what is the safe working current of this cable please?
 
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Here is a link to this TYPE of cable
http://www.prysmian.co.uk/export/sites/prysmian-enGB/attach/pdf/BS5467.pdf

in the details there are a number of nominal curent ratings.
Note there are options for in ground, in air and in duct.
There is no current rating for lying loose among the flower borders as that is not a recognised installation method.

Also, cable selection has many factors to consider. This cable may carry 30amps but, over a distance, the voltage drop may be considerable - it depends on the loads, distance, environment.

The process is not "I've got this cable how much can it carry"
The (very simplified) process is,:

first determine a load that needs to be powered,
then
what size of cable do the tables in BS7671 say I need
then
the load is xxx metres away from my power intake
what will the voltage drop be over xxx metres, do I need a larger size to meet the vd requirements,
etc
etc
etc

Go study cable calculation and selection topics.
 
lets clarify something..
the cable is rated for X amps..
this is regardless of the length of run and the type of OCPD etc, however these things do affect the choice of cable.

the length of run affects the volt drop only and since there is a limit on that then you may need bigger cable for a certain load

the OCPD is chosen based on the load and the cable then chosen based on that, you may need bigger cable for a different type of OCPD for example.

the other things asked for however do influence the rating of the cable

either way, according to the red book ( don't have access to the specific data for the BS number you gave ), 2 core 1.5mm² regular SWA is 22A for free air, or buried and not grouped with other cables.

so I wouldn't go higher than a 20A breaker or fuse, and not more than a 15A BS3036 semi enclosed fuse
 
With a 50m length of 1.5mm cable, volt drop will be a significant problem, so the total allowable load will be rather small, probably only 5 amps or so.
 
got some "SWA BS5467 2 x 1.5mmsq" whats the max current rating assuming its mains voltage please?
As long as it's Low or Extra-Low, voltage is irrelevant.


A ball park figure would do me
Why only a ball-park? How are you planning to use the cable such that you don't have to do the design work properly?

If it's going to an outbuilding are you aware of the issues surrounding exporting a TN-C-S earth to a location with extraneous-conductive-parts, if that's relevant?

Are you aware that the installation of it will be notifiable?

What about testing? Do you know what tests you would carry out on the cable and any final circuits it supplies? - what sequence you'd do them in and at what point you would energise the cable etc, and for each test do you know what is being measured, why it is important, how you would carry out the test, and with what equipment, and what sort of results you would expect to get if everything was OK?


lying on the ground
Illegal.


, and what type of overcurrent protective device it is connected to. -- This is partly what im trying to determine.
As Monkeh said - type, not rating.

ColJack's way of looking at it is correct, if starting from scratch, i.e. working out what size cable to use in a given situation, but if you're trying to determine the current carrying capacity of an existing cable then the type of protective device does affect that.


what is the safe working current of this cable please?
But actually I think you should get an electrician.
 
Thanks for all your help.

I would really like to understand the issue of voltage drop along the cable, but I am struggling.

The specification says that voltage drop is given in mV/ A / M (which I think is millivolt - Amp - Meters). The cable I have has a v drop of 31 mV/A/M. Just for example, if the load is 6A and the run is 50M then what is the voltage drop of the cable and what effect does this have on the current drawn for a 6A load please? My calculation for the voltage drop yeilds: 31 * 6 * 50 = 9300. This is less than 10 volts. Is it really a problem? I can appreciate that we now have less voltage to drive the load and hence slightly less current. I guess it matters what the load is in this respect, lets say that it is an electric motor bench saw (6A).

I appreciate that there is a lot more understanding behind this, but I am hoping that an example can demonstrate what the problem is. I am trying to understand why some answers in the thread only expected to be able to draw 3 Amp. (This is not a science competition, please feel free to ignore or approximate things that have very negligible affect).

I really do appreciate your help and time.
 
Some loads especially inductive loads such as motors have quite high starting currents.

If the supply cable is too small and the volts drop too high, the motor will not start.

Also lights will be dimmer and fluorescent lights will not strike
 
OP, don't try and convince yourself that it's OK to use this cable just because it's what you happen to have in the shed. Over that distance, about the only thing you'll be able to run off it is a couple of lights.

If you're planning on supplying an outbuilding such as a shed/workshop/gym/etc, you should be looking at 4mmsq as a bare minimum, and very likely larger depending on how you intend to use the building.
 
thanks RF. I understand about the inductive loads issue.

Should the calculation for the volt drop be doubled due to the return conductor as well? (The spec labels it as single phase AC touching) Not sure what AC touching means?
 

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