Sockets rarely get a survey’s full attention — the roof, the damp readings and the movement cracks take priority — but an accessible socket or two, particularly in an older property or a rental due an EICR of its own, is worth the thirty seconds a plug-in tester takes. It is not an electrical inspection. It is a quick, defensible way to notice the things a competent electrician would want to know about: no earth connection, live and neutral reversed, or an RCD that sits there doing nothing when the test button is pressed. Any of those is a one-line note in a report and a recommendation to get it looked at properly, not something to diagnose further on site.
The category splits on what the tester actually checks. A basic check plug — three or four LEDs, a fold-out or printed fault chart — confirms the socket is wired correctly and nothing more. Step up in price and the same plug-in format starts adding an earth loop impedance test, which gives a rough read on how good the earth path actually is, and an RCD trip-test button, which proves the protective device works rather than merely being present. That second tier is doing a genuinely different job: a socket that lights up “correct” on a basic checker can still sit on a circuit whose RCD does not trip, and only the fuller testers will tell you that.
None of this replaces a proper Electrical Installation Condition Report, done by a qualified electrician with calibrated test equipment and a certificate at the end of it. What a plug-in tester gives you is the evidence to know when that recommendation is worth making, rather than guessing. First, the one I’d buy.
The one I’d buy
Kewtech Loopcheck 107
Kewtech is a name that already turns up in a lot of trade test kit, and the Loopcheck 107 packs socket wiring, earth loop impedance, mains polarity and a 30mA RCD trip test into one plug-in unit, with the legend printed straight onto the case rather than a separate chart to lose. That is three distinct checks a basic check plug cannot do, and the RCD button is the one that actually proves the protective device is working rather than just present. It will not replace a proper EICR, but for a quick, defensible read on a socket during a survey, it is the most complete tool here that still fits in a pocket.
Typically £45–£60
Check price on AmazonHow I judge a socket tester
What it actually tests, not how many lights it has. A basic three- or six-light checker confirms the socket is wired correctly and nothing more. The genuine step up is an RCD trip-test button and an earth loop impedance reading — between them those tell you whether the protective device is doing its job, not just whether the cable behind the faceplate is connected the right way round.
An RCD button that actually trips something. Pressing it should cause a working RCD to trip within the regulation time. If nothing happens, that is the finding worth writing up — not a fault with the tester, and not something to explain away.
Indicators that do not need decoding. A fault legend printed on the case itself beats a fold-out chart that lives at the bottom of the tool bag and gets left in the van on the day it is needed.
A CAT rating appropriate for what is actually live. CAT II 230–300V is the baseline for anything plugged into a domestic socket outlet. It should be stated on the casing, not implied by the price.
Small, robust, and priced for what it does. Most of what separates a £15 tester from a £55 one is capability, not build quality. Buy the capability the job in front of you actually needs, not the most expensive unit on the shelf.
The comparison
| Model | Tests | CAT rating | Typical price | Best for | |
|---|---|---|---|---|---|
| Kewtech Loopcheck 107 | Wiring, loop, polarity, RCD | CAT II 230V | ~£45–£60 | Best overall | View |
| Socket & See SOK36 Professional | Wiring, loop, polarity, RCD | CAT II 230V | ~£55–£70 | Full-function alternative | View |
| Fluke ST240+ | Wiring, RCD, audible alert | CAT II 300V | ~£30–£45 | Trusted brand name | View |
| Martindale CP501 Classic Check Plug | Wiring only | CAT II 240V | ~£12–£20 | Best on a budget | View |
| Socket & See SOK34 | Wiring, loop | CAT II 230V | ~£45–£58 | Loop check without RCD | View |
| KAIWEETS HT106E | Wiring, RCD, LCD voltage | CAT II 300V | ~£13–£20 | Digital readout on a budget | View |
| Draper 34279 13A Socket Tester | Wiring only | 230V | ~£10–£16 | Cheapest in this guide | View |
The picks in detail
Kewtech Loopcheck 107
Best overall — wiring, loop, polarity and RCD in one unit
This is the top pick above, and it earns the place by doing more with one plug-in unit than anything else at a comparable price: a standard wiring check, an earth loop impedance test banded into good/check/urgent, a mains polarity check and a 30mA RCD trip test with its own button. Kewtech already supplies test equipment used across the trade, which counts for something when the reading needs to hold up if a client or an electrician asks how it was arrived at. The legend for all four tests is printed on the casing itself, so there is nothing to look up.
For
- Wiring, loop, polarity and RCD test in one unit
- Established UK trade test-equipment brand
- Fault legend printed on the case, no separate chart
Against
- Costs several times a basic check plug
- Loop-test bands are indicative, not a calibrated reading
Typically £45–£60
Check price on AmazonSocket & See SOK36 Professional
A full-function alternative to the top pick
Socket & See specialises in exactly this category, and the SOK36 covers the same four bases as the Loopcheck 107 — wiring, earth loop impedance, polarity and a 30mA RCD trip test — in a rubber-armoured casing built to survive a tool bag. There is no meaningful functional gap between this and the top pick; the choice mostly comes down to which trade name is already trusted, or which one happens to be in stock when the order goes in. It sits at the top of this guide on price, which is the only real mark against it.
For
- Same loop, polarity and RCD test spread as the top pick
- Specialist brand in this exact tester category
- Rubber-armoured casing built for daily knocks
Against
- Priced at the top of this guide
- No functional advantage over the Loopcheck 107
Typically £55–£70
Check price on AmazonFluke ST240+
The trusted brand-name pick
Fluke’s name carries weight well beyond electrical trades, and the ST240+ brings that reputation to a straightforward socket tester: a one-button RCD trip test with an audible tone alongside the correct/incorrect wiring LEDs, and a fault chart printed directly on the yellow casing. What it does not have is a loop impedance test, so it tells you less overall than the Kewtech or Socket & See picks above — it catches the same wiring faults and proves the RCD trips, but gives no read on earth loop quality. For a lot of survey work that is still enough, and the Fluke name is one a client is unlikely to question.
For
- Widely recognised, trusted brand
- One-button RCD test with an audible pass/fail tone
- Fault chart printed on the casing
Against
- No earth loop impedance test
- Tells you less overall than the two picks above it
Typically £30–£45
Check price on AmazonMartindale CP501 Classic Check Plug
Best on a budget
Martindale states the CP501 has sold in the millions, and it is easy to see why: three LEDs and a printed legend cover the basics — correctly wired, no earth, neutral fault, live-earth reversal — for a fraction of the price of the testers above it in this guide. It does not test loop impedance and has no RCD button, and the casing itself notes it does not detect every reversal fault combination, which is worth reading before assuming it catches everything. For a fast, cheap sanity check on an accessible socket, it remains the obvious default.
For
- Cheapest way to catch the obvious wiring faults
- Long-established, extremely widely used design
- Small enough to leave in every van
Against
- No RCD test and no loop check
- Does not detect every fault combination, by its own labelling
Typically £12–£20
Check price on AmazonSocket & See SOK34
A genuine loop check, without the RCD button
The SOK34 sits between the basic check plugs and the full SOK36: the same wiring checks as the budget picks, plus the good/check/urgent earth loop bands that the Kewtech and SOK36 offer, but no RCD trip-test function. That makes it a real step up from a Martindale or Draper for anyone who wants a loop reading without paying for the full four-test spread, though the saving over the SOK36 is modest enough that it is worth checking current prices before assuming this is the better deal.
For
- Adds a genuine earth loop reading over a basic checker
- Same trusted specialist brand as the SOK36
- Simpler than the full Professional model
Against
- No RCD trip-test button
- Price is close enough to the SOK36 that the saving can be marginal
Typically £45–£58
Check price on AmazonKAIWEETS HT106E
A digital readout, at close to check-plug money
Where the Martindale and Draper picks give a pass/fail LED and nothing else, the HT106E adds an LCD panel showing the actual mains voltage alongside the usual wiring-fault indicators, plus an RCD test button — all at a price close to the basic checkers rather than the professional testers. KAIWEETS is a newer name in UK electrical test kit than Martindale, Kewtech or Fluke, so it has less of a track record, but the specification on paper does more than a basic check plug for very little extra outlay.
For
- LCD voltage readout alongside LED fault indicators
- Includes an RCD test button at a budget price
- Compact and light
Against
- No earth loop impedance test
- Newer brand, less established than the trade names above
Typically £13–£20
Check price on AmazonDraper 34279 13A Socket Tester
The cheapest tester in this guide
Draper is a recognisable name off any DIY shelf, and this is the same basic proposition as the Martindale pick — correct wiring, reversed polarity, no earth, neutral fault, shown across a small bank of LEDs with the legend printed on the casing. It does not do anything the CP501 does not also do, and the saving over that pick is small rather than dramatic, but it is a perfectly reasonable spare to leave in a second bag or hand to someone else on site.
For
- Cheapest tester in this guide
- Widely stocked, recognisable brand
- Covers the same core faults as the budget pick above
Against
- No RCD or loop test
- No functional advantage over the Martindale CP501
Typically £10–£16
Check price on AmazonWhat actually matters — and what doesn’t
The real upgrade is RCD and loop, not more LEDs. A basic three-light checker and a fancier six-light checker tell you almost the same thing — the wiring is or is not connected correctly. The tester that earns the extra spend is the one with a genuine RCD trip button and a loop-impedance reading, because those are the checks a basic checker cannot do at any price.
A socket tester is not an EICR. It flags things worth writing up — no earth, reversed polarity, an RCD that does not trip — but it does not replace a qualified electrician’s proper testing with calibrated instruments and a certificate at the end of it. Treat a bad reading as the reason for a recommendation, not as the finished diagnosis.
A digital readout is a bonus, not a reason to pay double. An LCD voltage figure is a nice-to-have. A unit with LEDs only that has an RCD button and a loop test tells you more than a unit with a screen that has neither.
Loop-test bands are a guide, not a certified figure. The traffic-light “good/check/urgent” system on a plug-in tester is indicative. If it says urgent, that is the referral to make, not a number to write into a report as if it came from a calibrated loop tester.
Things worth ignoring on a listing: “professional grade” with no stated CAT rating anywhere on the page, and “multi-function” that turns out to mean it also comes with a carry pouch rather than any extra electrical test.
Questions I get asked
Can a socket tester replace a proper electrical inspection?
No. A plug-in socket tester is a spot check on one outlet at a time — it can tell you a socket is wired correctly, that the earth loop reads within a rough band, or that an RCD trips when tested, but it is not a substitute for an Electrical Installation Condition Report carried out by a qualified electrician with calibrated equipment. Its value on a survey is knowing when that recommendation is worth making, not replacing the person who would actually make it.
What does it mean if a tester shows “no earth”?
It means the tester has not detected a continuous earth connection at that socket, which on an older installation can be a genuine safety issue rather than a false reading. It is worth trying a second nearby socket to rule out a one-off connection problem at that outlet specifically, but a repeated “no earth” result is exactly the kind of finding that belongs in a report with a recommendation for a qualified electrician to investigate.
Do I need the RCD test button, or is a basic checker enough?
For a fast sanity check on wiring — is this socket obviously wrong — a basic three-light checker like the Martindale or Draper picks does the job at a low price. Where the extra spend earns its keep is proving that the RCD protecting a circuit actually trips rather than merely being fitted, which a basic checker cannot tell you at any price. On rented property, older installations or anywhere RCD protection is doing real work, that distinction is worth the extra cost.
What is the difference between a socket tester and a voltage tester?
A socket tester is a fixed-format plug-in device that checks one 13A outlet’s wiring, and on the fuller models its earth loop and RCD, in one go. A voltage tester is a handheld probe used to prove a circuit is dead or live before work starts, and covers far more than sockets — junction boxes, light fittings, isolators. The two do different jobs and most electrical work ends up needing both rather than one instead of the other.
A socket tester earns its place for the same reason as most of the kit in this series — it turns a hunch into something worth writing down. On a building survey or a retrofit assessment, that is often the difference between a vague note about “dated wiring” and a specific recommendation an electrician can act on. If you need a survey anywhere in Sussex, Kent or Surrey, get in touch — or browse the rest of the field-kit guides, including the voltage tester guide this one sits alongside.
Disclaimer. This guide is general information, not a substitute for a proper electrical inspection by a qualified, registered electrician. Prices are indicative, move constantly and were checked at the time of writing; the linked page always shows the current price. As an Amazon Associate I earn from qualifying purchases.