If you are thinking of buying a cable avoidance tool (CAT) there are a number of questions that you should consider. There are lots of CATs available and some are very good, but as with most things, others are not so good, and still others that – to use the old expression – I wouldn't want to touch with yours.

If you have good product knowledge and are familiar with the latest models of CATs, you probably do not need to read any further. However, if you are new to the business of searching for underground utilities or have not been in the market for new CATs for some while it can be difficult to know exactly what sort of tool you need for your particular situation. There are a lot of different models out there.

Of course, a CAT should always be used in conjunction with a signal generator (Genny). A CAT on its' own in Power mode can only detect live power cables with current actually running through them. This is fine if you are working in a street at night and have to locate the cables supplying power to the street lamps: you should have no trouble finding them. However, if you come back tomorrow morning when it is light and survey the same area you most probably won't find them. It does depend on the type of street lamps installed, but the likelihood is that they will not show up.

It follows that if you know for sure that you will always be trying to locate only power cables and that you know that they will always have power flowing through them, then there is an argument for saying that you only need to use a CAT. However, how many people can say that with assurance? This is why you always need to use a CAT and Genny together.

The next question is whether you want to be able to ascertain the depth of a service. Some CATs can only pinpoint the line of a utility but not the depth. The more advanced models available today can give you a depth reading as well. Again, it's a question of if you know that you will only ever have to dig down to a depth of a foot, then you may not need one which shows the depth. In fact, one of the ten commandments of ground-breaking is that you should dig down to a depth of a foot and then undertake a further check because there may be cables further down that were not detectable from the surface.

Another thing to consider is the distances over which you need to detect. Most CATs when used in conjunction with a Genny operate on two frequencies of 8khz and 33khz which are industry standards. However, some of the latest equipment emits two further frequencies which can detect signals over much longer distances. This is extremely useful and can save an awful lot of time out on site if you have to cover a large area, as in a highway survey for instance. The more advanced models will cost a bit more, but the savings when out on site can be considerable.

Another thing to consider is the area in which you will be working. Many main contractors have preferences for certain makes of tools, and some insist that you use certain tools for cable avoidance. One example is Network Rail which has a list of approved tools. If you use one which is not Network Rail approved, you will be removed from the site. Most of the CATs available today ARE Network Rail approved, but it may be something that you need to take into consideration.

The same thing applies to Gennys as well. You could be using an approved CAT, but an older model Genny which is not approved, so you will run up against the same problem. Some main contractors will also want to see a calibration certificate before you undertake any surveys.

Whatever else you do, when buying a CAT for your own use or for that of your employees, ensure that you or they take a proper training course. There is far more to undertaking utility surveys than simply buying a CAT and Genny and reading the instructions.