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,Green/Red

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

Product ID: 557085750

Details

Brand
KLEIN TOOLS
Colour
Multi
Item Weight
0.26 Pounds
Power Source
Corded
Style
Receptacle

📊Backlit LCD for clear voltage & wiring readout

⏱️Trip time display for precise GFCI testing

🛡️CAT II 135V safety rating for reliable protection

€ 81.42

Duties & taxes included

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Description

⚡ Test Smarter, Work Safer — The Pro’s Choice for Electrical Confidence

AUTO HOLD CONVENIENCE - Capture readings effortlessly in tight or hard-to-reach outlets—because your time is valuable.
BRIGHT LED INDICATORS - Green and red LEDs give you immediate visual confirmation of wiring conditions—no second-guessing.
PRECISION GFCI TRIP TIME - Measure exact trip times to troubleshoot GFCI devices faster and smarter than ever.
CRYSTAL CLEAR LCD READOUT - Instantly see voltage and wiring status with a large backlit display—no guesswork, just precision.
NEXT LEVEL FAULT DETECTION - Patent-pending tech spots open neutral and ground faults, elevating your safety game.

The Klein Tools RT250 GFCI Outlet Tester combines a large backlit LCD, precise trip time measurement, and advanced fault detection to ensure your 120V electrical outlets and GFCI devices are wired safely and functioning perfectly. With a CAT II 135V safety rating and user-friendly features like auto-hold and bright LED indicators, it’s engineered for professionals who demand accuracy, speed, and reliability on every job.

Specifications

ASIN	B08QW7K1JJ
Best Sellers Rank	#377,050 in Home Improvement ( See Top 100 in Home Improvement ) #564 in Multi Testers
Brand Name	KLEIN TOOLS
Colour	Multi
Customer Reviews	4.8 4.8 out of 5 stars (10,941)
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 Centimeters
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
Maximum Operating Voltage	120 Volts
Measurement Type	Voltage Tester
Minimum Operating Voltage	120 Volts
Model Number	RT250
Number of Items	1
Part Number	RT250
Power Source Type	Corded Electric
Specification Met	CSA
Style Name	Receptacle Tester
UPC	092644693212
Unit Count	1 Count
Upper Temperature Rating	60 Degrees Celsius

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