If people bring electrical equipment into your workplace you need to make sure their equipment is safe; ask to see their PAT testing certificate.
For example contractors or mobile discos coming into a hotel, such as in the example below.
Dave set up on the Saturday afternoon in the dance hall and left his gear there, plugged in whilst Steve and Anna had their Wedding Breakfast. The evening was a success, everyone had a great time and the disco was superb, even granny got up for a dance.
It was about 4am when the night porter started to smell burning wafting through the hotel; he had a look around but couldn’t work out where it was coming from at first, until the fire alarm went off – the panel said the alarm had been triggered in the dance hall.
After the fire brigade put out the fire, luckily it hadn’t spread, but it was clear that Dave’s gear was the cause of the fire. It turned out Dave didn’t know whether it was safe – he kept it in his shed, and had never had it PAT tested. When the hotel applied to their insurance company for funds to cover the damage they were told that their insurance wouldn’t pay; Dave couldn’t afford to cover the costs either.