Query CAT scan for utilities

[Chris Heath]

Hi, first post here. I'm in the process of swapping out a lead water main for MDPE and replacing Cast iron and clay drainage. I've hired a CAT and genny to try and locate the existing utilities, but I'm not sure about the results.

With the genny attached, the services seem easy to detect, but they all appear to be on top of each other. The services start in the right place, so I am reasonably happy that the genny signal isn't unexpectedly hopping across utilities, but I kind of expected some separation.

It is a 1920's property with lead water main, lead jacketed electric cable and steel gas pipe. The last utility that went in appears to be the gas, but there doesn't appear to have been much concern about separation, as the gas meter was just 2cm from the fuse box.

Is it normal that utilities in older houses are all on top of each other?

I'm going to dig a couple of test pits to confirm location and ensure I am reading the CAT right before I return it to the hire company. One concern is that the external stop cock for the communication pipe is not inline with the apparent path of the supply pipe.

 

[Chris Heath]

I've a bit more to go on here. Test pit has confirmed gas pipe and bricks for electric. There is what looks like a red painted steel pipe, just under the gas pipe at 35cm depth. Can anyone confirm the suspicion that this is an old gas pipe? Or is there any chance this is a water pipe that changes to lead before it enters the property?

 

[Hugh Jaleak]

Possibly an old Gas service, but common practice was to insert the new plastic gas pipe through the old steel service to avoid digging a trench or moling. (Gas People have a habit of moling through sewers, times I've seen a CCTV survey to ascertain why a sewer keeps blocking, only to find a gas service straight through the pipe....)

Not impossible it could be water, but I'd expect the water supply to have been laid in one or another, i.e. all steel or all lead. My money would be on gas, although whether it is redundant or not I wouldn't like to say....

 

[ianmcd]

Possibly an old Gas service, but common practice was to insert the new plastic gas pipe through the old steel service to avoid digging a trench or moling. (Gas People have a habit of moling through sewers, times I've seen a CCTV survey to ascertain why a sewer keeps blocking, only to find a gas service straight through the pipe....)

Not impossible it could be water, but I'd expect the water supply to have been laid in one or another, i.e. all steel or all lead. My money would be on gas, although whether it is redundant or not I wouldn't like to say....

I am going to up the stakes and say it is an old electricity cable, either way you need to get them out to check, usually free, the detectors arent great Im afraid

 

[Deleted member 267285]

Inclined to agree with Ian, I’d say electric cable, given it’s red and the presence of the bricks.

 

[Harry Bloomfield]

'Electricity bricks' are supposed to be laid directly over the top of the cable and those look recent, so I would suggest not your electric supply. I would favour it being an old gas pipe. Our original pipe was steel, but they replaced it with new plastic following a totally different via route front of house. The old steel they left in situ, at the rear.

 

[Chris Heath]

Putting the genny on it, the signal can be traced to beyond the existing gas meter, then stops half way down what would have been the original kitchen. The water pipe has been traced now as going under the kitchen floor and exiting somewhere near the side door. Googled the heck out of it, but cannot find any reference to common usage of red steel pipe. I've put a query in to Cadent as to whether they can identify it as gas pipe. They have no record of the residential pipework routes on their charts.

I've not lifted the Electricity bricks, but I was kind of relying on the supply being 100mm under them. May be worth confirming. They are clean from the dig, the test pit was done with jet washer and workshop wet vac.

Regarding the flakiness of the detectors. I have found it quite accurate, and the depth detection has been pretty accurate when used with the genny, but I have some strange readings from the front of the property.

There is a signal for power detection starts parallel to the main route. It seems to start from nowhere, and can be traced towards the street, sounding a strike alert for near surface cables where the S is, but again, ends with no apparent termination. The main signal from, what is believed to be, the main supply, can be traced consistently. Switching to radio mode, the main signal can be heard precisely from street to meter, and there is no radio signal from suspect detection. I'm left wondering if it is a ghost signal, or some reinforcing in the concrete creating a fault reading. There is the possibility that a neighbouring supply wanders across the property. Thinking I'm going to need to another test pit to confirm.

 

[JohnD]

red cables and ducts are used for high voltage electricity. is the coating shiny plastic?

can you see any embossed lettering?

it seems odd to have it along a domestic house, though.

 

[Chris Heath]

Not PVC or otherwise and not shiny. Appears painted, there is pitting and corrosion in places, and a magnet clings strongly to the pipe.

Good idea to check for embossing, I will have a look in daylight. There is a lot of firmly attached debris to the pipe. It appears they didn't get the memo on soft fill when back filling it. The hole was a mess of glass slag, flint and scrap iron.

 

[JohnD]

I don't know if hv was painted red before plastic coatings and coloured polypipe came out. it must be 30 years ago or more.

I have an idea it used to be bituminous black, though one place I worked still had (disused) buried oak duct with busbars, filled with pitch.

(Russell Road, by the old coal power station)

 

[ianmcd]

Cat and Genny are absolute crap in this situation, I know you are proud that you hired one but the readings mean diddly squat

 

[Ian H]

If you are replacing the supply entirely you only need the start and end points.

 

[Chris Heath]

Cat and Genny are absolute crap in this situation, I know you are proud that you hired one but the readings mean diddly squat

I've found them really useful to be honest. The current covering is 150m2 of 3 to 4" concrete. I don't want to break this up until all the Building regs are approved for start. We still need to live and park here until then. I've only got the groundwork team booked for 2 days currently. They have a crap load to do, and the last thing I want is to lose time to needless damage to services. I've accurately found the danger services, with only a couple of 12" pits and the services actually being where the Cat said they would be. Also enabled me to trace the existing drains with a sonde.

They were under £100 for the week from ESS. Really good value for money in my opinion, with the alternatives being either digging trenches until they are found or asking the digger man to go easy, just incase.

The rogue reading is annoying, but it is exactly where I want the trench drug for the replacement main, so I will have a look at the groundstrike, just to be sure. Still better than randomly digging holes.

 

[Chris Heath]

If you are replacing the supply entirely you only need the start and end points.

It is part of a series of jobs. The cast iron soil stack is going, clay drainage is being replaced, outside power and lighting put in, an out building 40m away is being connected up for drains, water and power. 1.8m boundary wall going in. There is going to be a chap with a digger putting in trenches for the water, electric ducts, drainage and foundations. Being able to say what is in the ground currently helps plan his work and with the building regs submission.