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06/6/2018 at 1:25pm
Location: Durham
Outfit: Caravan and tents
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Joined: 25/5/2004 Gold Member 
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There seems to be an awful lot of people with very little understanding of how site electrics work, how MCBs work, how RCDs work and how they all work in conjunction with each other.
Even more worrying is that so many people with so little knowledge are giving so much advice to so many people -n no wonder site owners often struggle. Facebook is particularly bad for this.
It's also a little disturbing to see people who arent experts accusing site owners who run their sites day in and day out of talking nonsense.
This is going to be a lengthy post as it is a lengthy subject - apologies for that. It's also going be quite a harsh post - no apologies for that!
Firstly - anyone who relies on an MCB to 'inform' them that they have overloaded their pitch supply is being very inconsiderate to other site users as well as to the site owners. Moderate and calculate your usage to ensure that it doesn't overload. The MCB is really a 'final stage' rather than a first stop.
Yes you can trip just your pitch, all of the pitches connected to your post, all of the pitches in part of the site or the entire site. It isnt nonsense at all. I'll explain how later.
OK - RCDs do not protect against overload. These measure an imbalance between the Live and Neutral parts of the supply. If that imbalance exceeds the scope of the RCD then it operates and kills the supply. The supply will not be restored until reset. This means that in the event of a short circuit or sudden power drop it will trip - potentially life saving. If you touch a live wire then current will flow into you, the RCD should detect the imbalance in current and cut the power. Note that bit about sudden power drop because the RCD has an 'upstream' effect as well as a downstream one. In other words, if the power to a unit suddenly cuts it can also trip the RCD. In this case the supply won't be restored until the unit is reset. So - if your power suddenly goes off there is a possibility it will trip the RCB on the post or possibly in someone else's tent (I'll explain how later). If those people are out for the day and it is a hot day then they could come back to find their food spoiled. More importantly, many campers have special medical needs and medicine coolboxes could be affected causing a loss of medication. Not cool (pun intended)
The Mains Circuit Breaker (MCB) is the overload protection. However they are NOT accurate. They have both a delay and a tolerance.It is possible to trip the post MCB before tripping your own. Then see above re tripping the RCDs
Campsite power supplies have what is known as a redundancy. That means that a 10amp supply (for example) may not be 10amps. This is because the redundancy allows that all items won't be used at the same time (your domestic supply is the same). The Post supply also has a redundancy, based on the estimation that all 4 units plugged in will not all draw 10amps each at exactly the same time (even if they all draw 10amps at some stage). The post may be part of a Section - that will also have a redundancy. Then the site main supply will also have a redundancy.
Looking at that you can see that it is not an exact science which is why those who use campsites should take the time to learn how to calculate their usage and count what is being used. Campsite owners learn over time what works and what doesnt - for their installation on their campsite. For that reason it is just common sense to listen to the campsite owner. And yes, some campsite owners are more knowledgeable than other, and some know very little. They probably still know their site better than we do though
Another potential issue - if you have a 16amp hookup kit and your site supply is 10amp or 6amp then it doesnt take a genius to work out that the post, section or site supply is going to trip before your own MCB cuts in.
Ok - RCDs and MCBs. Strangely, connecting loads of RCDs in line is not a good idea but it is what we have to do. The problem is that if you put 5x 25mA RCD units next to each other and put a fault condition across and they will all react at slightly different speeds. Bear in mind we are talking milliseconds for them to work. RCDs typically respond in between 30 and 50 milliseconds. That's an incredibly fast response so it is easily possible for 1 to respond in 40mS, another in 45mS and another in 50mS. This means that it is quite possible for an upstream RCD to trip before your RCD does (although it may appear to be simultaneous). Bear in mind most campers use a cheap portable unit and the campsite uses professionally installed ones! So yes, tripping an RCD can cause other units to also trip.
Circuit breakers are the same. Because of their tolerances it may be that an upstream MCB is more sensitive than yours. As mentioned previously it is also possibly that yours won't trip first anyway because it has a higher capacity than the site supply. And as also mentioned before due to redundancy it could be that a supply trips before the 'official' limit depending on what other campers are currently doing. It's also possible that it wont trip. For example you might be drawing a very temporary 11amps from a 10amp supply and it might not trip, especially if other campers arent using their supplies at that stage.
So - the rated power supplies are nominal, not absolute.
RCDs don't all work at exactly the same time or sensitivity, so it is perfectly possible to trip upstream.
MCBs dont always trip at the exact capacity and it is also perfectly possible to trip upstream.
Depending on the site layout it is perfectly possible to 'take out' other supplies on your post, section or the entire site.
Please take the time to learn a little about power consumption, about capacity and please show respect and consideration for other site users (and the site owners) by not overloading your supply in the first place. And please, please dont accuse other people of talking nonsense without a full understanding of the subject yourself.
Site managers who make these claims don't (usually) do it for the fun of it. They do it to reduce the issues on site. If they've had problems before they are more likely to err on the side of caution which is sensible not nonsensical.
I've seen for myself (and heard from others) of idiots (sorry but thats the only word) who take their curling tongs, domestic kettles, 2kw multicookers, teppenyakis, toasters etc camping with them and leave them all plugged in and just use them without any regard for their total usage or for the site supply.
I also sadly saw a disabled child have to be driven to hospital due to his medication being ruined when the site supply was down. Although the supply itself was only down for minutes, due to the RCD kicking their supply his special coolbox had warmed up on a hot day and his medication had been ruined. Not all medication is available at local pharmacies - a lot of these special medications have to be ordered especially.
Apologies for the long post and less than sympathetic comments. I do genuinely believe that we all need to have the consideration and take the responsibility for our actions and to be 'competent'.
Post last edited on 06/06/2018 13:29:42
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A slightly younger Victor Meldrew
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