Fitting a motion sensor? Choose the right scaffold.

For a motion sensor going on the facade at six to eight metres you hire the Altrex RS51, the narrow version at 75 cm. A box like that rarely hangs in the middle of a flat front elevation: it sits on a corner, above a drive, beside a garage door or at the start of a side path. In those places you often have no more than a metre or a metre and a half, and then 75 cm is the difference between fitting and not. Other models are under hiring a mobile scaffold.

If the mounting point stays below six metres, the MiTower comes into the running as well: a tower 75 cm wide for one person, with a working height of 4.2 to 6.2 metres. For a sensor above a front door or a carport that is enough, and you put it up single handed. Are you working higher, or do you want somebody on the ground watching while you aim, then take the RS51. Those two are set against each other in the comparison of mobile scaffold and MiTower.

On the platform you have more with you than you would expect for such a small box: a cordless drill, plugs, a screwdriver, a length of cable, a junction box and a voltage tester. A deck 245 cm long gives you the room to lay that out beside you instead of stuffing it into your pockets. On top of that you work with both hands above shoulder height on a motion sensor, and then you would rather not be balancing on a narrow rung as well. A ladder simply cannot offer you that.

Do not measure to the gutter but to the point where the box will actually sit, because on this job that easily saves you a metre. With the motion sensor under the overhang of a second storey you come out at six to eight metres of working height. Reckon back from there: your deck hangs about 2 metres below that figure, since you bridge the last stretch with your arms. The page on a working height of 7 metres shows which build goes with it.

Take the ground under your wheels as the zero point, not the threshold of your front door. With a sensor above a drive that is a real difference, because a drive like that often falls away towards the street and your tower then stands lower than the house. A raised terrace or a garden that steps up shifts your starting point too. In doubt between two builds for work on the second floor, take the roomier one. Half a metre short costs you a whole build.

Choosing too tight is more of a nuisance here than on painting work. You have to drill with both hands, set a plug and then turn a small clamp inside a housing, and none of that works with your arms stretched over your head. Set your platform so the box sits at roughly chest height in front of you, and you see straight away which way the head is pointing. Stand too high and you look down on the top of it and cannot judge the lens.

Here is the odd part of this job. A motion sensor looks down at an angle across the area it has to watch, and that is precisely the strip where you put your tower. For as long as it stands there the sensor sees tubes and platforms instead of an empty path, and you cannot judge whether it covers the right ground. Take that into account when you position: you fit the box square in front of it, and you test from the side.

The practical side is more familiar. Under the four wheels you want flat, load bearing ground, and around them enough space to splay the stabilisers. A drive of block paving or a concrete slab path is fine, loose gravel or a grass verge is not. Look at what else stands round such a spot: the car you were trying to protect, a bin, a bike rack, the downpipe and a hedge on the boundary. On a sloping drive, levelling on uneven ground takes you further.

Think about the time of day as well. You test at dusk or in the dark, so there you stand beside the boundary with a lamp switching on and off. Let the neighbours know you are at it, certainly when the motion sensor looks over their side of the path. If the tower stands partly on the pavement, keep a way past clear and ask the council whether that is allowed before you reserve the mobile scaffold. A lamp that lights half the street wants aiming properly in good time.

The fitting itself is soon over: drill, plug, hang the box, wire it up and screw it shut. An hour all told, perhaps two if a cable still has to be run. Even so you do not hire the mobile scaffold for half a day, because the setting up can only be done once it goes dark. Fit in the morning, test that evening and correct the next morning. Two rental days is the realistic minimum for an hour of work, and three is more comfortable.

Count on the time the tower itself costs as well. Building to seven metres takes two people an hour to an hour and a half, dismantling a little less, and those are hours in which you are not working on the motion sensor. Hang several sensors round the house and a build comes on top per elevation, so you soon run to three or four rental days. Plan those moves one after another instead of spread over two weekends. That saves you a second booking.

Financially, planning generously is not bad at all. The full rate applies to day one alone; every day you stick behind it goes with 95% off, so the extra morning to adjust something after the evening test costs you next to nothing. Book the tower for a single day and find out at seven in the evening that the head points the wrong way, and it is of no further use to you. Judging a period is covered at working out your rental days.

The great advantage of a stand that stays put is that all three steps happen from the same place. Within the 245 cm of your platform sit the mounting point, the spot where the cable comes in and usually the lamp the motion sensor switches. So do not set the tower tight underneath the box but half a metre to one side, so that you stand at an angle to it and can see both the fixing and the position of the head. Then you need not keep leaning over.

The testing itself goes quickest with two of you. One walks the path the way the postman will, the other stands on the platform and turns the head a few degrees between rounds. That way you are done in a quarter of an hour with what you would never manage alone in one, because otherwise you climb the mobile scaffold up and down at every attempt. Agree how you will signal each other before it gets dark.

Do not underestimate the number of trips down. Forget a plug of the right size and you are on the ground again, and at seven metres that is no small effort. So take a box with an assortment of plugs and screws up with you, and a lamp for when the light goes. Combine the job with hanging an outside light if you can, then you hire the tower once for two jobs and save a whole build.

The mobile scaffold arrives as a counted set of loose tubes, braces and platforms. On this job that takes some getting used to: you have one small box to fit and a sizeable stack of aluminium on your drive. Point out a spot beforehand where that stack is not in the way of the car or of the neighbours. Order before 15:00 on a working day and the set is there the next working day, so on a Friday you can still arrange something for the weekend.

You say yourself when the set comes and when it may go again, and on this job you choose those days around an evening when you have time to test. Have it delivered the day before the fitting, then you build without hurrying. Building is your own work: two of you, the manual to hand and the video if you are unsure anywhere. Which tube comes when is in the guide to building the tower.

Afterwards you take the tower apart and we come to fetch it; lay the parts together complete at a point the driver can reach. Would you rather drive yourself, then the set can be picked up free by appointment in Amsterdam, provided your trailer or van takes the length. The amount for out and back is fixed per province and is listed with the cost of bringing and fetching. Count it in, because it applies per run and not per rental day.

The build you stand on is made to EN 1004, and its load class 3 rating leaves room for 200 kg on each square metre. For this job that is generous: you, a cordless drill and a bag of tools come nowhere near it. It is still worth knowing where the limit lies, certainly if somebody climbs up with you to look on. More about it is in the note on this scaffold standard. Two people at seven metres asks for calm in any case.

The standing rules apply to an hour of work too. Brake all the wheels before you step on, never move the tower while a person or tools are on it, and stop in strong wind. On this job the electrics come on top of that: switch the circuit off before you connect the wiring and check it with a voltage tester, even when you are sure that nothing is live. Working with power at height leaves little room for assumptions.

What really counts on this job is light. You test in the dark, and then the edge of your platform is suddenly hard to make out, as is the tool still lying on it. So stand a work lamp on the ground shining across the tower from the side and never work by feel. Clear everything off the deck before you climb down, the small items included. The rest of the rules for working at height does not change for it.