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Paperless Datasheet
Going green and protecting environment is manufacturers' responsibility. Each WatchfulEyE product has a link of downloading data sheet on its enclosure:

3D file download

Model & Ordering Code

Model Ordering Code MCOV/Uc Remote Contacts UPC/EAN Code
WTH-50/B+C/R/1P-275 US120234 275VAC YES (0) 811914030423
WTH-50/B+C/1P-275 US120224 NO (0) 811914030485
WTH-50/B+C/R/1P-320 US120235 320VAC YES (0) 811914030430
WTH-50/B+C/1P-320 US120225 NO (0) 811914030492
WTH-50/B+C/R/1P-385 US120236 385VAC YES (0) 811914030447
WTH-50/B+C/1P-385 US120226 NO (0) 811914030508
WTH-50/B+C/R/1P-420 US120237 420VAC YES (0) 811914030454
WTH-50/B+C/1P-420 US120227 NO (0) 811914030515

Certificates of Products

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More Package
Model with suffix WTH-50/B+C/R/1P-275 x2pcs x3pcs x4pcs
Ordering Code US120234 US120234x2 US120234x3 US120234x4
Model with suffix WTH-50/B+C/1P-275 x2pcs x3pcs x4pcs
Ordering Code US120224 US120224x2 US120224x3 US120224x4
Model with suffix WTH-50/B+C/R/1P-320 x2pcs x3pcs x4pcs
Ordering Code US120235 US120235x2 US120235x3 US120235x4
Model with suffix WTH-50/B+C/1P-320 x2pcs x3pcs x4pcs
Ordering Code US120225 US120225x2 US120225x3 US120225x4
Model with suffix WTH-50/B+C/R/1P-385 x2pcs x3pcs x4pcs
Ordering Code US120236 US120236x2 US120236x3 US120236x4
Model with suffix WTH-50/B+C/1P-385 x2pcs x3pcs x4pcs
Ordering Code US120226 US120226x2 US120226x3 US120226x4
Model with suffix WTH-50/B+C/R/1P-420 x2pcs x3pcs x4pcs
Ordering Code US120237 US120237x2 US120237x3 US120237x4
Model with suffix WTH-50/B+C/1P-420 x2pcs x3pcs x4pcs
Ordering Code US120227 US120227x2 US120227x3 US120227x4

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In accordance with: IEC/EN61643-11 - Class I+II and UL1449 Type 4 Location
Location of use: main sub-distribution boards, branch sub-distribution boards
One-piece compact design with minimized volume but maximized capability of Class I+II surge protection.
Internal thermal disconnect devices help ensure safe or at end-of-life
WTH-50/B+C/R/1P Series Technical Data
Requirement Class to IEC/EN61643-11 Class I+II
IEEE Category Rating C, B & A
Nominal Discharge Current (In) 25kA
Max. Discharge Current (Imax) 50kA
Pulsed Current (Iimp) 5kA
Protection Modes L-PE, N-PE
Protective Element High Energy MOV
Follow Current (If) NO
Response Time (tA) <5ns
Leakage Current (at 75%U1mA) <20μA
Thermal Protection YES
Protection Rating (IP Code) IP 20
Short Circuit Current Ratings (SCCR) 25kA rms
Max. Back-up Fuse (if mains >100A) 100A gL (circuit-breaker: <50A)
Surge Life at 3kA (8/20μs) >5000 events
Temperature Range - 40°F to 176°F (-40°C to 80°C)
Relative Humidity 0% to 95% noncondensing
Maximum Operating Altitude 10,000 feet (3000m)
Terminal Cross Section 35mm² (solid) / 25mm² (stranded)
Stripping Length Contacts 0.6inches (15mm)
Terminal Screw Torque Max. 3.5Nm
DIN Rail EN60715 35mm top-hat rail
Dimensions DIN 43880 20mm
Housing Material Thermoplastic (UL94 V-0)
Housing Design Compact design
Net Weight Per Unit 0.3Lb (136g)

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Surge Protection Connection Diagram

Maximum Continuous Operating Voltage (MCOV/Uc) 275VAC 320VAC 385VAC 420VAC
Voltage Protection Level (Up) 1.6kV 1.8kV 1.9kV 2.0kV
Residual Voltage (Ures) 1.0kV 1.1kV 1.2kV 1.4kV


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Remote Contacts (Dry Contacts)
1: COM (Common)
2: NC (Normally Close)

Contact Ratings 125VAC/3A, 250VAC/1.5A
Terminal Cross Section Max. 1.5mm²
Stripping Length Contacts 0.25 inches (6-7mm)
Remote Terminal Torque 0.25Nm

Fault Indication

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Common Terms and Definitions
1. Normal operating voltage rating (Un)
2. Maximum Continuous Operating Voltage (Uc/MCOV):
Maximum r.m.s. voltage, which may be continuously applied to the surge protective device's mode of protection.
3. Nominal Discharge Current for Class II Test (In):
crest value of the current through the surge protective device having a current waveshape of 8/20μs.
4. Maximum Discharge Current (Imax):
Crest value of a current through the surge protective device having an 8/20μs waveshape and magnitude according to the manufacturers specification. Imax is equal to or greater than In.
5. Voltage Protection Level (Up):
Maximum voltage to be expected at the surge protective device terminals due to an impulse stress with defined voltage steepness and an impulse stress with a discharge current with given amplitude and waveshape.
6. Residual Voltage (Ures):
Crest value of voltage that appears between the terminals of an surge protective device due to the passage of discharge current.
7. IEEE 62.41
CATEGORY C: outdoor overhead lines, service entrance (most severe)
CATEGORY B: major feeder, short branch circuits, service panel (indoor)
CATEGORY A: long branch circuits, receptacles (indoor) (least severe)

How to choose a suitable Uc(MCOV) value
Note: Uc >1.15Un
The relationship between two parameters Uc and Up of a surge protective device is proportional.
If Uc is small, the value of Up is also small; surge protective devices with smaller Up can provide better surge protection.
Whether to choose smaller Uc depends on the voltage stability of the grid.
If you choose surge protective devices with smaller Uc for the grid with instable voltage, the surge protective devices will frequently work while the grid voltage fluctuates, resulting in shortening surge protective device's product life.
If you choose larger Uc, and the value of Up is accordingly large, the surge protective efficiency will not be so fine.
If you are unsure of the voltage stability of the grid,
it is suggested to calculate MCOV(Uc) using the following formula: √ 2  Un < Uc < √ 3 Un

AC Network (Un) MCOV(Uc), L/N-PE Protection Mode
110V, 120/208V, 127/220V 150V
220/380V 275V, 320V, 385V
230/400V 275V, 320V, 385V, 420V
240/415V 320V, 385V, 420V
266/460V, 277/480V 385V, 420V
347/600V 550V, 690V
Wind Power System 690V (Grid side ), 885V (Gen side )

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AC Network Connection Diagram (1/2)

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AC Network Connection Diagram (2/2)

Difference mode & Common mode Connection Diagram

Common mode:L-PE, N-PE surge protection
Difference mode:L-N surge protection

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Selection of back-up fuse

Selection of back-up circuit-breaker

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1. Origin of the installation
2. Distribution board
3. Distribution outlet
4. Main earthing terminal or bar
5. Surge protective device, class I or II tested
6. Earthing connection (earthing conductor) of the surge protective device
7. Fixed equipment to be protected
8. Surge protective device, class II tested
9. Surge protective device, class II or class III tested
10. Decoupling element or line length
F1, F2, F3 overcurrent protective disconnectors
NOTE Refer to IEC 61643-12 for further information.

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N-PE Module
WTH-65/G+ module integrates High-Energy GDT, no leakage current. It pairs WTH-50/B+C/R series surge protector, combined into N-PE protection mode, the two modules are the same in dimension and shape, and are connected with a dedicated bus-bar to achieve a perfect combination.
WTH-65/G+ Technical Data
Max. continuous operating voltage (Uc) 255V
Nominal Discharge Current (In) 40kA
Max. Discharge Current (Imax) 65kA
Pulsed Current (Iimp) 22.5kA
Voltage protection level (Up) 1.1kV
Protection Modes N-PE only
Protective Element High Energy GDT
Follow Current (If) 100A rms
Response Time (tA) <100ns
Net Weight Per Unit 0.24Lb (109g)

3P + NPE Combintion Package
Model with suffix Ordering Code Model with suffix Ordering Code
WTH-50/B+C/R/1P-275 x3pcs +NPE US120234x3N WTH-50/B+C/1P-275 x3pcs +NPE US120224x3N
WTH-50/B+C/R/1P-320 x3pcs +NPE US120235x3N WTH-50/B+C/1P-320 x3pcs +NPE US120225x3N
WTH-50/B+C/R/1P-385 x3pcs +NPE US120236x3N WTH-50/B+C/1P-385 x3pcs +NPE US120226x3N
WTH-50/B+C/R/1P-420 x3pcs +NPE US120237x3N WTH-50/B+C/1P-420 x3pcs +NPE US120227x3N

1P + NPE Combintion Package
Model with suffix Ordering Code Model with suffix Ordering Code
WTH-50/B+C/R/1P-275 +NPE US120234x1N WTH-50/B+C/1P-275 +NPE US120224x1N
WTH-50/B+C/R/1P-320 +NPE US120235x1N WTH-50/B+C/1P-320 +NPE US120225x1N
WTH-50/B+C/R/1P-385 +NPE US120236x1N WTH-50/B+C/1P-385 +NPE US120226x1N
WTH-50/B+C/R/1P-420 +NPE US120237x1N WTH-50/B+C/1P-420 +NPE US120227x1N

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FAQ & Help
1. What should I do if I can't find the paper manual in the product packaging?
Watchful Eye products is committed to going green with paperless data sheets. On the side of each product enclosure is an engraved link with URL for downloading paperless data sheet and QR code of the website. If you need the paper data sheet, you can open the link and print the data sheet by yourself.

2. The advantages of fault indication windows?
If surge protection fails, the fault indication windows will turn red, thus it can be seen intuitively, and the surge protective device can be replaced in time to avoid damage to the equipment caused by a second surge.

3. What instruments can be used to test whether its surge protection function is normal or not?
Test with a Watchful Eye surge protector tester

4. Can you list more applications?
Power supply panel, whole house

5. What is the feature of Class I+II?
It provides high capability of Class I surge protection, and capability of Class II (equivalent to the parameters of WTH-40 ) fine protection with low residual voltage as well, applying to Class I and Class II surge protection in multiple areas. If you are not sure which module to choose for protecting your area, Class I + II is the best solution.

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After-sale Services
Watchful Eye provides a 5-year quality warranty globally.

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