Capacity Of Extension Cables

Typo? They may need to be upsized to avoid excessive voltage drop.

Thank you. You are correct.

No the tables will not include the volt drop from the distribution board to the power outlet. So unfortunately it's a case of large cross section extension leads to minimise the volt drop from the power outlet to the load.

U r right. These are well known facts. Don't be dependent on tables, instead I will suggest to make ur calculation as per cable manufacturers catalogue and cable laying conditions. Formulas are well known and available. Also, note as the cable size increases the impedance offered by cable decreases and also the voltage drop (R=rho x L / A). Also, for motor we need to consider additional factor i.e. Starting voltage drop in addition to running voltage drop. As motor draws 6 times (7.2 times max) current and our selected cable should be suitable for this condition. As per IEC-34 motor is suitable for voltage difference of +/- 5% to +/-3% during normal run. If you don't know the voltage drop formula let us know, we will guide.

Now for another thought. Let's assume the cable in the house running from the box to the receptacle is #12 AWG. There will be a very small voltage crop, depending on the length of run. Now if we plug in an extension cord, say 50 ft long,#12 AWG; there would be one voltage drop measured from the box to the end of the extension. Right? If I used a #10 AWG extension instead, there would be two voltage drops, one from the box to the receptacle and a second voltage drop from the receptacle to the end of the extension. Am I thinking right?

Here is another one; If I use two extension cords, one # 16 wire and the other #12, which extension cord would you plug into the supply first, the #16 or the #12? or would it not make any difference as long as the current draw was within the capacity of the smallest cord?

If I were using two different extension cable sizes. I would Use the Heaviest cable closest to the power source and the lighter cable closest to the user. Don't really know if it would make any real difference or not. But if you are over drawing on the lightest cable then I think it would be best to be able to keep a closer eye on that cable in case of trouble.

When voltage drops are calculated are the connections/Plug type and receptacle type taken into consideration or just the cable type & size?

Totally immaterial either way, the current through both will be identical!!! the thinner one will get proportionally warmer that's all.....

Unless of course the fire extinguisher for electrical fires is also near to your work area!!!Then you won't have so far to run!!!

hey Guys, this is simple Ohm's Law.......

A more important point is that unless the current is really tiny, any extension cord must be COMPLETELY removed from any storage drum, or even lying on the ground in a coil as it will dramatically increase the impedance and therefore the heating effect....

As this will probably happened to the one nearest the work area, this could cause major problems.......always extend an extender cord fully and lay any loose stuff around without forming a coil.....both extender cords if two are in use.....

Good point about uncoiling extension cords.

The extension cord manufacturer has no idea of the size or distance from your box to outlet, so they rate for the cord only. Mixing extension cord sizes regarding the order of sizes and lengths makes no difference to the output total voltage drop due to a given load. I always put the larger gauge first for the already mentioned reason (easier to monitor cord heating at the load).

In determining the proper type of power extensions to be used, AWG sizing and length of copper conductors are important but one must also take into consideration the type and condition of the connectors / receptacles where they will be connected to. Most of the time due to age, usages such wear and tear of existing of existing power outlets, should also be considered and included in your analysis! Due to contact resistances caused by poor mechanical /electrical contacts, large voltage drops are encountered on this alone. Also, for the same poor connection reasons, extending power often results to electrical fires hazards! I believe the importance of proper copper sizing considerations should go hand-in-hand with the type or mechanical conditions of the electrical connectors to be used in extending your electrical power anywhere!

Voltage drop : Resistance : Wire Size. It is also cumulative and current sensitive. Say you have three 25' cords, one 12 guage, one 14 guage and one 16 guage. The 16g has the most resistance as it is the smallest diameter. The 12g has the least as it is the largest. If you plug each into an outlet that measures 120 volts, the other end will also measure 120 volts. If you repeat this with a load on the end (an electric heater, perhaps), the 12 guage will measure less than 120 volts, the 14g less than the 12g and the 16g less then the 14g. If you need to use all three to reach 75' you should start with the 12g feeding the 14g feeding the 16g. Largest to smallest. This gives you the least total voltage drop. If you start with the smallest, it carrries the full load of the heater plus the heat-loss current of the other two cords. This can over-heat the small cord resulting in insulation break-down, arc-flash and lots of loud trucks with pretty red lights.

They all carry the same current, regardless of their order.

The smaller still has greater heat-loss and voltage-drop due to it's higher resistance.

So?

It (the thinnest cable) may "set the mode", but all cables have the same current flowing through them, no matter which cable has the highest losses......

Do you mean each one is plugged into a socket separately? Or one after the other in a long long line?

in the extension cords why don't they attach a label showing the various ratings of power(watts)and corresponding length(ft) for which it is suitable w/o causing excessive voltage drop. for eg: For AWG 12-x ft,for AWG 10-y ft,for AWG 14-zft and so on.

guys,

two issues,

One:in the UK we are coded by the IET (was the IEE), to produce an accepatble VD at all receptacles. Rememeber that in the UK all power circuits are run as 240Volt Ring Mains - with a few minor exceptions. Our code assumes 2.5 mm cable on House wiring. NB 4mm can be used for high power circuits, cannot remeber at his remove what the conditions are; I have used 4 mm for connrecting other distributionboards for example.

If you are running without the benefit of a Ring Main then you will get some VD at the Receptacle; get calculating and measuring! And also with 110Volts that can make matters worse, higher current for the same power.

Two: In the Uk, again, most Extension cords if not all, are rated, for the cable wound on the reel and the cable fully off loaded. Ideally one should not have to do all the arithmetic to use a standard piece of domestic kit!

Good luck

Sleepy

If 2.5mm^2 cable/wire is used for wiring 13A and 15A BS outlets, can we use 1 or 1.5mm^2 cable for 5A BS outlets?.

Provided the fusing reflects this it should be OK. But you must actually install per the electrical laws and requirements for where you live!

Due to people changing out sockets, its probably a better idea to use the heavier cable just in case the bigger socket gets installed at a later date. Better safe than sorry!

pnban,

Sorry, I thought that I had replied to you on this, apologies, I am having a few finger/keyboard problems!

1 In the UK 1.5mm cable can only be used for lighting circuits which are NOT Ring.

2 5A Sockets should NOT be used on Ring Mains unlesss they have some form of protection as otherwise a short on the 5A connection can compromise the Ring. 13A sockets have individual fuses on each plug outlet - 13A or smaller.

3 The only exception for 2 pin plugs is the Shaver connection which I assume is a fail safe through its transformer? 110v/230V.

4 The extension Cable sitting in my Garage which i am about to use in anger is rated at 700 Watts , cable wound on, and 3200 watts , cable fully unwound. This has two sockets but the rating above is for the sum of both.

Hope that this helps

Sleepy

pnban,

hallo again, just a few minor points.

1 The extension reel that I used this afternoon had the above rating; it was a 30 metre lead on a (approx) 12" diameter reel. It was 2/3rds unwound and had a near continuous load of abt 800Watts for about an hour. There was no appreciable additional warmth in either the wound or unwound portion.

2 I have never had to measure VD in a domestic situation, (except for fault finding situations). I am protected by the UK system which assumes that I put kit together following their rules and with parts that are appropriately qualified and labelled.

3 15A sockets are no longer available in the UK. The great benefit of the 13A socket is the obligatory requirement that every plug inserted into a 13A receptacle must be appropriately fused for the appliance, max rating 13A! But can and should be reduced for lighter loads.

4 It is important to follow the Ring System for Power circuits, you can have multiple rings, as have I - each Ring must be suitably and separately fused.

5 I use separate rings for upstairs, downstairs and my study whilst the Garage/workshop has its own power rings fed from a separate distribution box.

6 I also have an additional Power ring for my garden, very useful when working outdoors.

This could carry on but that should be sufficient!

Enjoy

Sleepy