Light tower wind rating: what actually holds a mast up

The kilogram figure is not a wind figure

A load rating is the static mass a support holds at full extension with a head mounted. It covers the head, the balloon and the hardware at the top, and it leaves a margin that movement spends rather than weight. A 12.8 kg head on a mast rated at 40 kg is not a 27 kg allowance for wind, because the wind does not push down.

What the wind does is bend the mast and rotate the base. A 100 cm balloon at the top of a 4.8 m mast is a sail on a lever, and the force up there is multiplied by the distance to the ground. That is why two supports built from the same tube can carry different ratings, and why the load figure on its own does not tell a buyer whether the tower will stand.

The mast is a lever, and height is the multiplier

The tripod range shows the effect without any theory. The 2.0 m and 2.8 m tripods are rated at 20 kg, the 3.8 m and 4.0 m tripods at 80 kg, and the 4.8 m mast at 40 kg. Nothing about the tube got weaker at the top of the range. The same head sits further from the ground, so the same push produces a larger moment at the legs.

That is the number to read before the brochure number. A crew that wants the head above the plant, the hoarding and the parked plant is asking the mast for height, and every metre of it costs stability that has to be paid back in ballast, in a wider base or in a shorter mast.

What each support is rated for

The head weights run from 1.9 kg on the 60 W head to 12.8 kg on the 1400 W one, so every head in the range is a small share of the 40 kg rating at 4.8 m. The rating is not there for the lamp. It is there for the lamp plus everything the weather adds, and a longer lever spends that allowance faster than a short one does.

Ground, ballast and the surfaces that catch buyers out

A tripod needs a surface that holds a foot without creeping. Compacted hardstanding and concrete are the easy cases. Soft sand, fresh asphalt and a cambered verge are the three that catch buyers out, because a leg sinks or slides and the mast leans before the wind has done anything at all.

Ballast belongs on the legs or on the frame, low and spread, and never hung on the mast. A cart answers the same question differently: the small, medium and large carts weigh 16, 28.5 and 48 kg with braked wheels and stabilisers, so the mass that holds the tower down is also the mass that has to be pushed into position.

What to ask for, in writing

• The wind speed the support is rated to with that head mounted at full extension, and whether the figure changes with the balloon size.
• The ballast or the anchors the supplier expects for the surface on the site, in kilograms.
• The mast section the rating applies to, because a figure for a half raised mast is not the figure a crew will use.
• The gust at which the balloon comes down, and who on site is watching for it.
• The difference between IP54 and windproof, which are unrelated properties and often quoted in the same sentence.

The sequence that keeps it standing

Inflate at ground level, raise the mast last, and lower it first. A balloon inflated with the mast already up is a sail being raised in the worst possible order, and a unit that goes up in two minutes in calm air takes two people and a ladder in a gust.

Take it down at the end of the shift rather than leaving it standing overnight. A tower left up is a tower that meets the weather nobody scheduled, and a balloon left out in high wind is a damaged fixture whatever the IP number says. The same rule covers the extras: a banner, a sign or a cable tied to the mast adds sail area that the rating never included.

A wind rating is only useful with the head, the height and the ballast beside it. Ask for the four as one figure, and treat a supplier who quotes a wind speed without asking which head is mounted as a supplier who has not read the sheet.