Size of "extension cord"

[sunnybrook]

As there appears to be a forum for "professional" electricians, I guess amateurs can post here. Also, although the question refers to using a product in Bulgaria (230v, 50hz), I guess the theory would apply in the UK, so bear with me please...

We brought a log splitter back from the UK and it works beautifully but we have a question about the electrics. We have emailed the manufacturer and seller but they have not responded.

It has a 2200W motor. It is designed for European market as the built-in cable has a European plug. It comes with a 10m extension cable with European socket and UK plug. Changing the plug is no problem.

We have used it no problem close to the house. We would now like to use it near the garage, which is about 18m further than the provided cable will reach. Max. permissible cable length, according to the manual, is the 10m cable provided (2.5 sq mm, we assume, as that is the rated cable for it).
They say.."A longer cable impairs the motor performance and consequently the function of the log splitter." We assume that is because of voltage drop but, are there other factors?

If we had a 20m run of (radial) cable circuitry in the house walls and plugged their extension cord in at the far end, supposedly that would be acceptable. It may sound naive but what is the difference between that and running a 18m cable from a socket at the house, which is 2m from the supply, and then plugging their extension cord into a socket attached to the end, so long as the thickness of the cable used is appropriate (or, even, replacing their cable completely with a 28m run of cable of appropriate thickness).

So, what thickness would be required, in that case? The best we can buy locally is 3.6 sq mm stranded 3 core, although it is expensive, and all the tables that we have read on voltage drop seem to imply that that is really no worse than their 10m of 2.5 sq mm.

Thanks

 

[WarrenG]

Hi Sunnybrook,

Even though fully qualified I am no real expert in motors but I will try and help.

A motors speed is a product of voltage while the torque is a product of the current. Upon energizing the motor, a low voltage is applied and a high current to generate the torque required for starting.

The motor will rotate and efficiency is found between voltage, counter EMF & current. Once this is found the current drops.

In a low voltage situation the current is unable to drop into a efficient state while it maintains its operational limits.

So technically the motor would be constantly running at a maximum torque which would be extremly inefficient and cause heat generation. This heat increases resistance in the field windings of the motor and damages the motor brushes, armatures etc.

Of course this all boils down to the actual percentage of voltage drop for your intended cable run but I believe this is the reason for ......"A longer cable impairs the motor performance and consequently the function of the log splitter."

The manufacture maybe just covering theirself by limiting the cable for pure efficency?

Here is a quick online calculator for voltdrop which you can try.

Cable Size Selector Calculator and online cable selector for electricians

Hope this helps!

Warren

 

[sunnybrook]

Thanks for the response.

As I mentioned in the op, I had looked at several online voltage drop tables. The link that you provide, although useful, only indicates minimum cable size and shows a specific voltage drop, in this case 1.5mm with drop of 7.2V, which I would have thought was high. Unfortunately, it doesn't generate cable size based on specific voltage drop, i.e. so you could compare the 3.6 sq mm cable that I have seen with the 2.5 sq mm that they say is minimum.

The cable that I have seen has what appears to be a heavy rubber exterior with three 3.6 sq mm stranded and other tables that I have used would suggest that that would be a suitable substitute at 28m length for a 2.5 sq mm cable at 10 m. Unfortunately, although this is Bulgaria, it is still expensive at £2.20 per metre. Still, I can always use it for other electrics around the garden.

Thanks again.