KeefySher said:
I hope that's a typo and you mean 220 x Amps, not 220 divided by Amps.
Here's the sticky out tongue thingy
I hope that's a typo and you mean 220 x Amps, not 220 divided by Amps.
Here's the sticky out tongue thingy
JamesH said:
Hello James something else must have happened becasue an MCB (miniature circuit breaker) is a current sensitive device and it will only trip if the current passing through it rises above it's threshold value, unless of course it is faulty.
On the basis that most caravan appliances present essentially a set resistive load to the circuit that does not change significantly with change of voltage (microwaves are rather more complex) then, the basic Volts = Current x Resistance rearranged to Current = Volts / Resistance would show you that as the voltage fell so would the current also. This would not trip an MCB.
Caravans are also fitted with an RCD (Residual Current Detector). These use the principle that wherever you measure the current in a series circuit it will be the same. So it should be the same in the Live and in the Neutral connections. If it isn't the same then it means there is a current leakage, which usually means an appliance or the wiring has gone faulty. Usually this means there is risk of a mains electric shock. The RCD in a caravan should designed to trip if the fault current reaches 30mA for more than 200mS.
Some (but not all) RCD's will also automatically trip out if the supply voltage is significantly reduced or cut completely. These always need to be manually reset when they are first connected to a mains power source, or after a power cut. Perhaps your caravan was fitted with one of these and it dropped out when the it saw the supply voltage was reduced. I have been unable to find the dropout voltage for these products, but I would be surprised if it was as high as 215V for a nominal 230V supply.
So what happens if there is a constant load attached to the electric motor that is being supplied by the voltage? (not that you will get this situation in a caravan).
WoodlandsCamper said:KeefySher said:
I hope that's a typo and you mean 220 x Amps, not 220 divided by Amps.
Here's the sticky out tongue thingy
Indeed it was, strange how I'd put an x in the line below. The emojis are still not back, and auto correct is still not working.
Are you by any chance using an ipad or similar? Icons are OK using a desktop PC.
Edit - I don't think I've ever had auto-correct, but spelling mistakes are still notified by the wavy red line underscore.
Edit - I don't think I've ever had auto-correct, but spelling mistakes are still notified by the wavy red line underscore.
WoodlandsCamper said:Are you by any chance using an ipad or similar? Icons are OK using a desktop PC.
Edit - I don't think I've ever had auto-correct, but spelling mistakes are still notified by the wavy red line underscore.
I'm using Safari browser on a Mac Book Pro running ElCapitan, that run auto correct, no red wavy underscore, the correct spelling of the word in blue text as you type. Not sure if the recent maintenance on here has had an effect as it's only on posts post the maintenance I've experience loss of emojis (icons? My daughter reprimands me if I don't call them emojis) and spelling errors.
Ditched the PC a long time ago.
I've just come to this thread - what fun. Must have every math and physics teacher banging their head against a wall.
Somewhere along the line someone asked what happened if the electric motor had a load attached to it. Well, it all depends. In industry most drives will be 3 phase not single and for a big inertial load will be started in one configuration and then once up to speed switched to another - commonly called star/delta - starting in star and then switched to delta ( I think- long time ago so may be the opposite). This sort of thing does not occur much in caravanning !!
What may occur is that the switch on/ inrush current of some devices e.g. microwave ovens may just be enough to exceed the rating of the caravan RCD if you have lots of other things connected at the same time. Incandescent lighting exhibited this problem but you needed a lot of bulbs to cause it.
Fortunately my sphere of 'expertise' is light current pneumatics measurement and control, leaving the heavy power stuff to my colleagues, who had to worry about things like maximum demand tariffs, lightning protection etc. I too have CEng followed by some alphabet spahgetti accumulated over a long and varied career, but have always found our chosen hobby provided the essential ' back to basics, relief.
Somewhere along the line someone asked what happened if the electric motor had a load attached to it. Well, it all depends. In industry most drives will be 3 phase not single and for a big inertial load will be started in one configuration and then once up to speed switched to another - commonly called star/delta - starting in star and then switched to delta ( I think- long time ago so may be the opposite). This sort of thing does not occur much in caravanning !!
What may occur is that the switch on/ inrush current of some devices e.g. microwave ovens may just be enough to exceed the rating of the caravan RCD if you have lots of other things connected at the same time. Incandescent lighting exhibited this problem but you needed a lot of bulbs to cause it.
Fortunately my sphere of 'expertise' is light current pneumatics measurement and control, leaving the heavy power stuff to my colleagues, who had to worry about things like maximum demand tariffs, lightning protection etc. I too have CEng followed by some alphabet spahgetti accumulated over a long and varied career, but have always found our chosen hobby provided the essential ' back to basics, relief.
Just a couple of facts from BS 7671 amd3
1 reg 708.530.3 states caravan pitch shall not be more than 20 m from the supply pillar
2 reg 721.55.2.6 States a flexible cable of continuous length of 25m + or - 2m shall be used. For 16 amps a minimum of 2.5mm.
So if you need to use more than 25m of lead,then the caravan site you are on does not comply with the relivent British Standards go and ask them who did there last Electrical Installation condition report..
1 reg 708.530.3 states caravan pitch shall not be more than 20 m from the supply pillar
2 reg 721.55.2.6 States a flexible cable of continuous length of 25m + or - 2m shall be used. For 16 amps a minimum of 2.5mm.
So if you need to use more than 25m of lead,then the caravan site you are on does not comply with the relivent British Standards go and ask them who did there last Electrical Installation condition report..
GStockton said:
I'll tell them the next time I'm in France and more than 25 m from a bollard. I'm sure they'll be totally embarrassed.
With regard to the CLs that I've been on I chose to pitch more than 25m from the bollard. I could have pitched next to it had I so desired.What have the French got to do with our British Standards? It is up to you how far you pitch away from the Bollard. But you should be no more than 20m
Parksy
Moderator
GStockton said:
Some years ago before I learned anything much about caravanning we stayed on the then newly refurbished C&CC site at Chertsey.
I don't know if things have changed since, but our pitch was so far from the ehu bollard that we had to borrow an extra ehu cable (with a £10 deposit) from the site warden.
The fact that these extra ehu cables were available suggested that our situation was a regular occurrence.
The grassed bank areas had been newly seeded so all around us was bare soil and I remember not being particularly happy with the pitch that we were given.
If only I'd known then what I know now.
All you need to remember is an electrical device is given a power rating at a given voltage, so if the voltage drops so does the power rating.
In the past i've had 250 volts at home during this time my kettle rated at 2200W at 230 volts ac, had noticably more power.
In the past i've had 250 volts at home during this time my kettle rated at 2200W at 230 volts ac, had noticably more power.
Power (wattage ) will always stay the same even if the voltage changes, ampage will change which will then determine how quick your kettle will boil.
You are missing the point again, wattage WILL NOT stay the same. If voltage reduces then power/wattage will reduce. See earlier post re label on Morphy Richards kettle where they give 2 different wattages for the 2 voltages they quote.
viz. The same kettle is rated 3 kw at 240v, but only rated 2.52 kw at 220v.
Only Resistance stays (roughly) the same. Wattage is (Volts squared)/Resistance. Current doesn't come into the equation.
Think of a filament light bulb. The less voltage you apply to it the less bright it is, ie the less power (in the form of light) it is producing. A kettle element is only a big filament in water. and acts the same
viz. The same kettle is rated 3 kw at 240v, but only rated 2.52 kw at 220v.
Only Resistance stays (roughly) the same. Wattage is (Volts squared)/Resistance. Current doesn't come into the equation.
Think of a filament light bulb. The less voltage you apply to it the less bright it is, ie the less power (in the form of light) it is producing. A kettle element is only a big filament in water. and acts the same
To amplify Woodlands answer;
In basic electric circuits (and heating elements are very basic) the power in Watts can be calculated by the linear equation:
Watts = Volts x Amps
However the current (Amps) is proportional to the voltage and is determined by the resistance (R) of the load in Ohms
Amps = Voltage/Resistance (Ohm's Law)
Virtually all the high powered electrical appliances in caravans are heaters of some kind. Heating elements are basically resistances (Ignoring the resistive change with temperature) then the resistance of these appliances will remain basically unchanged. But if the Volts change then by Ohm's Law the current will change proportionally and then by simple maths the power dissipated at any voltage can be calculated in Watts.
In basic electric circuits (and heating elements are very basic) the power in Watts can be calculated by the linear equation:
Watts = Volts x Amps
However the current (Amps) is proportional to the voltage and is determined by the resistance (R) of the load in Ohms
Amps = Voltage/Resistance (Ohm's Law)
Virtually all the high powered electrical appliances in caravans are heaters of some kind. Heating elements are basically resistances (Ignoring the resistive change with temperature) then the resistance of these appliances will remain basically unchanged. But if the Volts change then by Ohm's Law the current will change proportionally and then by simple maths the power dissipated at any voltage can be calculated in Watts.
Thanks WC and Prof. School boy days Funny how those things stick in your memory
So back to the OP by using two cables of 25mtrs would I be correct in saying the Potential Difference has also doubled? If that was the case then the voltage would halve and I'd be getting 115volts
I suspect apart from the latest 2011 regs saying 25mtrs is the max the actual voltage reduction over 50 mtrs isn't much greater than 25mtrs.
Has any one measured the respective voltage outputs between the two?
Funny how those things stick in your memory So back to the OP by using two cables of 25mtrs would I be correct in saying the Potential Difference has also doubled?
If that was the case then the voltage would halve and I'd be getting 115volts I suspect apart from the latest 2011 regs saying 25mtrs is the max the actual voltage reduction over 50 mtrs isn't much greater than 25mtrs.
Has any one measured the respective voltage outputs between the two?
The cable is only part of the resistive circuit and voltage drop will be proportional. If the resistance of the cable is significantly lower than the resistance of the load then most voltage drop will be across the load.
Edit - this could lead (excuse the pun) on to the topic of heat dissipation in EHU cables and the need to uncoil them. :evil:
Edit - this could lead (excuse the pun) on to the topic of heat dissipation in EHU cables and the need to uncoil them. :evil:
I've used two cables a few times on CL's to get more space to myself, never had any problems due to voltage drop, but never in winter.
Only thing i've ensured is the plug and socket is covered to keep them dry and visible, even put them on bricks to avoid possible water pooling.
Only thing i've ensured is the plug and socket is covered to keep them dry and visible, even put them on bricks to avoid possible water pooling.
This issue of cable length needs to be put into perspective. Every length of cable that carries current will produce a Voltage drop. If you use a longer cable for the same current you will experience a bigger voltage drop, But in reality we are talking about an 25M EHU add ing 0.72 of an Ohm to the system resistance. If you were pulling the full 16A that would only equate to an 11.5 volt drop, but the voltage drop is proportional to the current draw, so if you were only pulling 4A the volt drop on the EHU cable would be 2.9V
Don't forget that there will be inherent resistance in all the sites wiring, and how long is that?
In reality the voltage drop caused by an EHU cable should not by itself compromise the operation of a caravan.
Don't forget that there will be inherent resistance in all the sites wiring, and how long is that?
In reality the voltage drop caused by an EHU cable should not by itself compromise the operation of a caravan.
ProfJohnL said:
Thank you Prof. :cheer:
At last we get the answer to the OP.
A relieved Grumpy old dog. B)
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