Is it ok to use this tester for the 20a power outlet (not gfci)?

A Very good question, since the device name starts with GFCI. Answer is YES, because despite the name, the device is mainly a regular outlet tester, checking cross wiring, missing wiring, and reporting voltages, all worthwhile tests for non-GFCI outlet. Also works with 15amp & 30amp with adapter. Thanks for the question.

Most of the outlets in the basement where i'm living say >6.00 when i test them. are they wired wrong? is it safe to use the outlets?

It is not safe to use those outlets. If an outlet is good, the green light on the tester should illuminate, and the display should register a voltage close to 120 volts.

Is this accurate enough to measure with some confidence which is the most upstream receptacle in a circuit for choosing gfci location?

Resolution accuracy inadequate for that task. Displayed digits determines resolution. In this case, meter accuracy will not be and can not be better than +/- 1 volt because digital resolution is always +/- 1 in the least significant digit. Example: If measuring a true, standardised 120 volts, meter might display 119V (-1), 120V or 121V (+1) if calibrated/adjusted correctly. You've got the right idea, but this meter displays only 2-1/2 digits (120V). You will need a meter with 3-1/2 (120.0V) digits displayed. Worst case resolution at 120 volts will then be ~0.1V (100 mV). You need to see those millivolts differences. Get one with stated accuracy and preferably calibrated. Cheers!

What will happen if you press the gfci test on a non gfci? will it do nothing. or will it trip the breaker in the panel, and i have to flip the switch

The amber lights on the tester will blink, nothing will trip.

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Klein Tools RT250 GFCI Outlet Tester with LCD Display, Electric Voltage Tester for Standard 3-Wire 120V Electrical Receptacles

Klein Tools RT250 GFCI Outlet Tester with LCD Display, Electric Voltage Tester for Standard 3-Wire 120V Electrical Receptacles

Product ID: 756166332

Details

Brand
KLEIN TOOLS
Colour
Multi
Item weight
0.26 Pounds
Power source
Corded
Style
Receptacle

📊Backlit LCD for clear voltage & fault readout

⏱️Precise GFCI trip time measurement

🔴🟢Bright LED indicators for instant wiring status

R$819

Duties & taxes included

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Sold byAmazon BrazilDelivered byDesertcartCustomer service byDesertcartReturns14 days · 30 with PRO

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Description

⚡ Test Smarter, Work Safer — The Klein RT250 Has Your Back!

TRIP TIME PRECISION - Measure GFCI trip times accurately to troubleshoot with confidence and speed.
AUTO HOLD CONVENIENCE - Lock readings effortlessly on hard-to-reach outlets, making every test hassle-free.
PRO GRADE SAFETY RATED - CAT II 135V rating ensures reliable, professional-level electrical testing every time.
ADVANCED FAULT DETECTION - Patent-pending tech spots open neutral and ground faults others miss—boosting safety.
CRYSTAL CLEAR LCD DISPLAY - Instantly read voltage and wiring faults with a large backlit screen, even in dim job sites.

The Klein Tools RT250 is a professional-grade GFCI outlet tester designed for North American 3-wire 120V receptacles. Featuring a large backlit LCD, it clearly displays voltage, wiring faults, and GFCI trip times. Its patent-pending detection system identifies open neutral and ground faults, while bright LED indicators provide instant visual feedback. With an auto-hold function and a CAT II 135V safety rating, this compact, durable tester delivers precise, reliable diagnostics for electricians and serious DIYers alike.

Specifications

ASIN	B08QW7K1JJ
Best Sellers Rank	705,379 in DIY & Tools ( See Top 100 in DIY & Tools ) 792 in Circuit Testers
Brand	KLEIN TOOLS
Colour	Multi
Customer Reviews	4.8 4.8 out of 5 stars (10,978)
Global Trade Identification Number	00092644693212
Included Components	2 x 1.5V AAA Alkaline Batteries and Manual
Item Dimensions	11.5 x 2.9 x 5.1 centimetres
Item Length	4.5 Inches
Item Type Name	Klein Tools RT250 GFCI Receptacle Tester with LCD Display, for Standard 3-Wire 120V Electrical Outlets
Item Weight	0.26 Pounds
Item Width	2 Inches
Manufacturer	Klein Tools
Manufacturer Part Number	RT250
Maximum Operating Voltage	120 Volts
Measurement Type	Voltmeter
Minimum Operating Voltage	120 Volts (AC)
Model Number	RT250
Power Source	Corded Electric
Specification Met	CSA
Style Name	Receptacle Tester
UPC	092644693212
Unit Count	1 1
Upper Temperature Rating	60 Degrees Celsius

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