Hot weather and breakdowns: panels, motors and chillers

It's the third hot day in a row. At 3pm the line's main drive trips on overtemperature. The fitter opens the panel and a wave of heat comes out. The cabinet fan is turning, but the filter behind it is grey with dust. Someone props the door open and points a desk fan at it. The drive resets. It runs till 4:30 and trips again.

Across the yard the chiller is on high head pressure for the second time today. In the compressor room it's like an oven.

Most of the time, heat doesn't cause new faults. It finds the weak spots that were already there. A clogged filter, a tired fan or a dirty condenser coped all spring. On a hot afternoon, it doesn't.

The panel is the first thing to go

Drives, PLCs and power supplies all have a maximum ambient temperature on their data sheet. Many drives derate above a set temperature, which means they give less current before they trip. On a cool day there's headroom. On a hot one, a drive that was running close to its limit has none.

So the first check is airflow, not the drive.

• Are the cabinet filters clean? Most sites change them on a calendar. In dusty areas, a calendar isn't enough.
• Is the fan actually moving air? A fan can spin and still be clogged.
• Is anything blocking the vents? Pallets stacked against a panel are common.
• Is the panel near a heat source, like an oven, a compressor or a south-facing wall?

Don't prop panel doors open as a fix. You lose the protection the enclosure gives, you let dust in, and you leave live parts open in a walkway. The law expects electrical kit that's exposed to "the effects of the weather, natural hazards, temperature or pressure" to be built or protected so it doesn't become a danger (Electricity at Work Regulations 1989, regulation 6). A hot panel with the door wedged open fails that test on more than one count.

If a panel runs hot every summer, it needs a proper fix. That could be a bigger fan, a filter fan with more flow, or a panel air conditioner. A thermal camera on a hot afternoon will show you which panels are worst. Our post on thermal imaging for electrical panels covers how.

Motors and overloads

Motors run hotter on hot days. That much is obvious. What catches people out is how little it takes to tip a marginal motor over.

Check the fan cowl first. If it's packed with dust or fluff, the motor isn't cooling. Check the fins. Check the motor isn't in a corner where hot air from something else blows across it.

Then think about the overload. A motor that trips on a hot afternoon may not be faulty. It may have been running near its limit all year. If someone's tempted to turn the overload up, stop them. Find out why it's drawing the current first. Our guide to a motor tripping on overload has a checking order. If it's a drive tripping rather than a starter, see inverter trips on overcurrent, overvoltage and earth fault.

HSE's code of practice for PUWER makes the link between this and safety. It gives the example that "failure to lubricate bearings or replace clogged filters might lead to danger because of seized parts or overheating" (L22, paragraph 70).

Chillers and compressors work hardest when it's hot

A chiller has to dump its heat into the air outside. The hotter that air, the harder it works. A dirty condenser coil, a failed condenser fan or a short refrigerant charge might not show on a mild day. On a hot one, the chiller trips on high pressure or can't hold the temperature.

Your team can check some of this. Is the condenser clean? Are all the fans running? Is anything blocking the airflow, like a skip parked in front of it? Is the chiller recirculating its own hot air?

But know where the line is. Anyone working on the refrigerant side needs their own F gas qualifications, "even if you work for someone else" (GOV.UK). That covers servicing, maintenance and leak checks on refrigeration and air conditioning. If you use the equipment, you're also responsible for getting it checked for leaks (GOV.UK). How often depends on the gas and how much is in the system*.

So have the out-of-hours number for your chiller firm ready. If the chiller protects product, know what you'll do while you wait. Our post on a chiller going down covers that.

Compressors are the same story. Hot intake air and a hot compressor room mean high discharge temperatures and trips. Check the room ventilation and the cooler. Hydraulic power packs suffer too, and our guide to hydraulic oil running hot has the checks.

Your engineers get hot too

Panel rooms, roof plant and compressor houses get very hot in summer. Your engineers work in them.

There's no legal maximum. HSE says "there's no law for maximum working temperature, or when it's too hot to work" (HSE, temperature in the workplace). But indoor workplaces must still have a reasonable temperature during working hours (Workplace Regulations 1992, regulation 7). HSE lists boiler rooms among the places where heat stress can happen. It also points out that work rate, humidity and work clothing all add to the risk (HSE, heat stress). A fitter in arc flash PPE in a hot switch room ticks every box.

So plan the hot jobs for the cool end of the day where you can. Make sure there's water to hand. And don't send someone up to the roof plant alone at 3pm in a heatwave.

Make summer part of the PPM

Here's our view. Hot weather breakdowns are mostly planned maintenance that slipped.

The code of practice says how often you maintain should take account of the "operating environment" (L22, paragraph 72). It also says extra measures may be needed where hard conditions "are foreseen or have been experienced in use" (L22, paragraph 76). You've had hot summers before. They're foreseen.

So build a summer list and run it in May. Filters, fans, condensers, cowls, room vents. It's cheap work. It's a lot cheaper than a line stopped for the afternoon while you wait for an engineer who's on three other hot-weather jobs.

What to do on Monday

1. Change or clean the filters on every drive and PLC panel, and check every cabinet fan is moving air.
2. Walk the chillers and compressors with the fitter: condensers, fans, room vents and anything blocking the airflow.
3. Check you have the out-of-hours number for your chiller and compressor firms, and that the engineer they send holds F gas qualifications.
4. Add a summer check list to the PPM for next May.

* F gas qualification rules and leak check intervals correct as of 31 August 2026. Check GOV.UK F gas qualifications and GOV.UK leak checks for the latest. Paragraph numbers refer to L22, fourth edition (2014, amended 2018).