What Is Covered, and When
Knowing What Should Be There
Locating is easier when you know what a street is likely to contain before you switch anything on. This session is the background: how UK distribution is arranged, what is underfoot in an ordinary road, how telecoms and water and gas are laid out around it, and what the surface gives away if you read it.
Eleven Thousand Volts Under an Ordinary Street
Walk down an average street and the distribution running under it is predominantly eleven kilovolt, feeding substations that step it down to the low voltage network people actually connect to. That is not exotic infrastructure in a special location. It is the normal arrangement in the normal road, under the footpath people park on.
Joint Bays, and Why an Earth Is Not Always an Earth
At joint bays the cables are connected together, with links between the joints, and that changes what happens when you apply a signal: it will travel further and into more services than the drawing suggests. There is a related trap on earthing. A cable can have an earth in the electrical sense and still not offer the return path a transmitter needs, which reads on site as equipment failure and is nothing of the sort.
High Voltage in Close Company
Where several high voltage cables run close together, tracing becomes genuinely difficult rather than merely awkward. Signal goes onto one and onto the next, the fields distort each other, and without access to the individual cables there is often no clean answer. The session is candid about it, which is more useful than a technique that only works in a diagram.
Telecoms Has Its Own Logic
Telecoms is laid out to a pattern worth knowing. Connections to properties sit in the duct nearest the boundary line, and fibre tends to run nearest the road. A sweat tee is not a tee shape at all, it is closer to a Y, and it heads for the nearest cabinet. Knowing the pattern tells you where to look before the locator tells you anything.
Reading the Surface
A great deal is written on the street if you know the notation. Marker plates and posts carry letters indicating the feature, H for a hydrant, SV for a sluice valve, and so on, along with figures giving distances. Old plates still carry the names of organisations that no longer exist, which is a dating tool in itself. None of it is a substitute for a survey, and all of it tells you where to start.
Yellow Marker Tape Is Not Detectable
One assumption worth killing on the spot. The yellow tape laid over a gas main is an identifier, not a conductor. It is not a copper strip and you cannot put a signal into it, and a surprising number of people believe otherwise. Polyethylene pipe itself is porous, which is why in contaminated ground or a high water table a membrane-wrapped pipe is used instead. None of that gives an electromagnetic locator anything to find.
Where the Gas Service Runs, and What Gives It Away
Every gas company will tell you the same thing: where the service enters a property, it takes the shortest route from the main to that point. If you can see the entry and you know roughly where the main runs, you have the line without instrumentation. The modern independent gas providers are also fitting service indicators, and a green cabinet on a concrete base with a lock on it is a piece of apparatus rather than street furniture, whatever it looks like.
A Word on CPS Mode
Some manufacturers sell a cathodic protection mode as the way to find high pressure pipelines. In genuinely rural ground it works, but so does a standard receiver on power or radio. Elsewhere it behaves close enough to a power mode that relying on it alone is risky, and transmission crews have been trained on it without being told that. Clipping on and applying a signal remains the more reliable answer.
Also in the Knowledge Hub
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