Too Much Coffee

Can anyone explain to me (in words a non-electrician can understand!) just exactly why Behmor issue the warning about not using an extension cord?

I would have thought that as long as the extension was up to taking the current that is used, then voltage etc would remain relatively unchanged. Or am I missing something?

I'm guessing that because it must be very close to the 13 A domestic rating, and that a usual extension cord has a multi plug at the end letting you plug more stuff in. It's easier to say 'don't use one' than to make the user work out the current through the entire socket and make sure they aren't using more than the 13 A.

Also some extension cords have a max current rating when wound up and when at full extension - another variable that I'm guessing Behmor don't want to get involved with!!

Maybe someone else can shed more light on this, but 240 AC is 240 AC and a few meters of 13 A rated extension cord shouldn't matter if the load (your roaster) is rated at drawing less than 13 A. Unless you want to plug 4 into the same extension

Yep, I think it is Behmor covering their backsides, and avoiding the risk of people using unwound reels or damaged extensions. Nowadays as a installation test finishes at the socket and there is no PAT testing on domestic appliances(or extensions) it would be foolish for any company to give advice other than "Plug directly to mains wall socket"

Behmor is 1600w so in the UK, it is only asking for 8a or so. (1600/230). In the states the amps would double.

The longer the extension the higher the resistance, so long cables will cause a voltage drop. This can be mitigated by using cable with larger diameter conductors or keeping the cable cool. Voltage drop is bad for roasters.

Is the warning a safety one or could they be thinking about performance

lsjms wrote: Is the warning a safety one or could they be thinking about performance

The warning is affixed to the mains cable, and states that using an extension can increase roast times and consequent risk of fire.

Thanks for the responses so far>

Copper wire is a conductor, but it is also a resistor. The longer the cable the greater the resistance and the greater the drop in voltage at the appliance. Most extension cords are not of adequate conductor diameter to carry a load of 13 Amps. If you really need to use an extension cord you would do well to make one using cable with heavier cross-section conductor (3mm square or more) and use the best plugs available. Better yet, wire a heavy cable into the socket rather than using a plug. The voltage drop using a standard extension may be 20% or more.

Of course the Behmor needs nowhere near 13a.

"Most" 13a extension cords have 1.5mm(or 1.25) x section conductors
Assume its a long one at 25m

(mv/a/m)x amps x length in m / 1000
28x13x25/1000 = 9.1v

As % - 9.1/230x100=3.95%

.05 under the UK acceptable maximum voltage drop for supply to circuit outlets and nowhere near 20%. 20% would be totally unacceptable and cause significant damage to drill motors etc.

Your supply voltage(Europe) may be +- 10% @230v. The fact that our suppliers may issue us with any thing from 207 - 253v and still be within limits is a bigger issue for electric roasting (sans Variac) than extension issues, but obviously if you roast on extension at a time of low supply voltage those beans will be in for a baking and your components may revolt.

Pardon my ignorance, but's what's a Variac?

GeoffsCigars wrote:Pardon my ignorance, but's what's a Variac?

Variac is a name that used to be a trademark of a US company. It refers to a variable autotransformer that is really nothing more than a coil of wire with the insulation removed from a portion so that a slider can make contact with the individual windings. In practice this looks like a round box with a knob on top which one can turn to vary the output voltage. In contrast to an electronic dimmer a variac produces a pure sine wave just like the input source meaning that it can be used to vary the line voltage directly. A variac for a relatively high wattage heating element is large, heavy and relatively expensive. They are often available on ebay.

The important bit in Bruce's detailed response is: "a round box with a knob on top which one can turn to vary the output voltage". The rest is just to show of the wealth of his knowledge acquired as a result of his age

Variacs can be extremely useful for roasting (I know that Phil used to make extensive use of one, not sure if he still does). I'd run some tests first though to see how consistent your roasts are, before considering investing in one.

Personally Geoff, I'd send Steve an email, as he will likely be able to clarify what is a legal requirement and what is a practical concern. I've spoken with him about this kind of stuff in the past and it never ceases to amaze me, the extent to which we are "nanny'ed" by ruling bodies, and supposedly for our own good!

The main issue for most of us around here is going to be the risk of "baking" beans (as mentioned above) due to overly long roast times. If you were thinking of using a long, cheap, extension lead to roast in a draughty garage during the winter, then that would be best avoided! If you only want to add on a metre or two (to what is an unfortunately short lead (due to EU regulations apparently)) in order to position your roaster under an extraction hood, then I think you should be fine. I did find that my roast times were extended if I had my breadmaker running at the same time (but that may just be the old wiring in my house).

Gouezeri wrote:If you only want to add on a metre or two (to what is an unfortunately short lead (due to EU regulations apparently)) in order to position your roaster under an extraction hood, then I think you should be fine. I did find that my roast times were extended if I had my breadmaker running at the same time (but that may just be the old wiring in my house).

Yep. That is exactly what I do, and have done this ever since I got my Behmor almost a year ago now. A short cord like this (I use a 2 metre cord rated at 13A) keeps voltage loss to a tiny amount, gives me a bit more flexibility in positioning and without any noticeable difference in roasting performance.

That warning on the Behmor cord is a bit like the advice that you shouldn't swim on a full stomach. Reasonable advice perhaps if you are going to swim in open water, but perhaps a bit OTT if you are just paddling in a few inches of water!

Now THAT has to win the crappest analogy of the year award surely. Where's my prize?

No prize for you. Your analogy is perfect. The swimming full thing is as crazy as saying extensions are dangerous.

That said I rate your chances of a good roast at 207v about as high as Michael Phelps winning after eating a dozen Crispy Cremes.

lsjms wrote:That said I rate your chances of a good roast at 207v about as high as Michael Phelps winning after eating a dozen Crispy Cremes.

i can confirm that (not anybodies swimming performance that is). in our old house i used to see voltage swings between below 200V and up to 230V. i got

bruceb wrote: a round box with a knob on top which one can turn to vary the output voltage

and together with a fluke i was able to control the voltage to a more reasonable and constant 220V-230V. i didn't try to create fancy roast profiles by using the variac. it's just that roasting with the hottop at 198V wasted quite some nice beans...