portable appliance testing, and that's self explanatory.Responding from the USA here, I have no idea what a pat test is, that said I've never done 400 of anything in one workday.
In an ideal world, as your visit is booked in on site, the customer has arranged for each department to collect all their appliances in a convenient location where the confirm the presence of all items against last year's list, delete retired items and add new items to the test schedule. Then you can swiftly visually inspect them, check the plug top and fuse and carry out the required tests. You then log the results and apply a passed test sticker.
In reality, you turn up and they "didn't know you were coming", last years results are not available and you spend the rest of the day crawling round under desks trying to locate everything you can before doing the above. Fine if you have a pantyhose fetishism but otherwise a right pain in the proverbial.
The 400 a day dreamer will have all the managerial and organisational skills of a seagul so you can guarantee you wont be getting the "ideal world".
You'll be selected for the role on two criteria.
1, You DGAF and will sticker any thing that stands still long enough.
2, You are inexperienced and will work your --- off to achieve the impossible only to see the shortfall down you your own failings and cut corners in an attempt to keep up.
The second is particularly insidious as it destroys good people's confidence and work ethic and ultimately turns them into the first.
I very occasionally do them, when one of our major clients have let a site lapse and are running round panicking. We charge day rate and make no guarantees on 'tests per day'. It gets done at the rate of a person who hates doing it and doesn't have the speed of regular practice. Their requests are getting more infrequent, either they've upped their game or are going elsewhere, both are a win as far as I'm concerned.