Section 13 — Electrical

Neutral Grounding Resistors

IPE Engineering Practice IPE-EP-13-10-1

Document number: IPE-EP-13-10-1 · Section: 13 — Electrical

1.0

1.1

1.2

1.3

1.4

2.0

3.0

3.1

3.2

3.3

3.4

3.5

3.6

SCOPE

This Practice describes high and low resistance neutral grounding resistors. The resistors shall be solidly connected between ground and the wye points of transformers.

This Practice is appropriate for attachment to an inquiry or purchase document when accompanied by the referenced IPE Engineering Practices and completed Data Sheets, EP 13–10–1 DS.

Any deviation from this Practice must be approved by the procedure described in EP 1–1–3. A revision bar indicates all changes made to this Revision.

REFERENCES

All applicable sections of the latest standards and codes listed below are a part of this Practice unless amended herein:

STANDARDS AND PUBLICATIONS

IPE Engineering Practices
EP 1–1–3 Deviations to IPE Engineering Practices EP 13–10–1DS Neutral Grounding Resistors Data Sheet
ANSI/IEEE Standards
32 Standard Requirements, Terminology, and Test Procedures for Neutral Grounding Devices C57.13 Requirements for Instrument Transformers

DEFINITIONS

Contractor – Company or business that agrees to furnish materials or perform specified services at a specified price and/or rate to the Owner.

Inspector – A Inflection Point Engineering, LLC appointed engineer or inspector.

Manufacturer – The recipient of a direct or indirect purchase order for materials and/or equipment. In this context, a direct order is one issued to a Manufacturer by a Contractor or the Owner. An indirect order is one issued to a Manufacturer by a vendor (recipient of a direct order) for materials, fabricated components, or subassemblies.

Owner – Inflection Point Engineering, LLC .

Owner’s Engineer – A Inflection Point Engineering, LLC appointed engineer.

Purchaser – The party placing a direct purchase order. The Purchaser is the Owner’s designated representative.

SERVICE CONDITIONS

Low resistance grounding resistors shall perform satisfactorily when operated outdoors in an atmosphere typical of petroleum plants. Unless noted otherwise on the Data Sheet, the resistors shall be used in a 120ºF maximum ambient, –15ºF minimum ambient, and at an altitude of 3300 feet or lower.
High resistance grounding resistors shall perform satisfactorily when operated outdoors, as specified in paragraph 4.1 above, as well as indoors when supplied as part of a low voltage MCC/switchgear assembly. The resistor shall be capable of operation at the maximum internal temperature of the equipment enclosure (MCC/switchgear) with the equipment at full load, the resistor operating at maximum fault current and at a 120ºF ambient.

DESIGN, CONSTRUCTION AND MATERIALS

Basic Construction
General: Each resistor shall be completely factory assembled, indoor or outdoor type and suitable for the mounting specified, e.g., level concrete pad, metal stand, transformer mounted, or MCC/switchgear enclosure mounted.
Resistor Enclosure
Each resistor enclosure shall be completely fabricated from copper free aluminum screen, angle and sheet materials.
All assembly hardware shall be series 300 stainless steel or cadmium plated (corrosion resistant).
The resistor shall have a safety enclosure designed to prevent entrance of rodents and birds as well as protection against physical contact of the resistor by humans.
When installed in a classified area, resistor temperature rise shall not exceed 80% of the autoignition temperature of the combustible gases, vapors associated with the hazardous environment.
High Resistance Ground Resistors
Each resistor shall be stainless steel edge wound or wire wound type.
Resistor shall be suitable for use in the classified area specified, and shall be equipped with a stainless steel nameplate so stating.
High resistance ground resistors shall be rated for continuous operation at rated current.
The resistor connection points shall be enclosed and have provisions suitable for user connection of number 8 AWG wire. Typical ratings are shown in Table 1.
Low Resistance Ground Resistors
Low resistance ground resistors shall be stainless steel edgewound or wire type. Stamped grid resistor element types are not acceptable.
Resistors shall be capable of carrying the specified current for 10 seconds without exceeding 760ºC rise above a 30ºC ambient per ANSI/IEEE Std 32.
Bushing connections shall be suitable for the cable/wire specified.

Unless specified otherwise, low resistance ground resistors shall be sized to limit the ground fault current to 400 ampere. Typical ratings are shown in Table 2.
The resistor frame support base insulators shall be porcelain pin and cap type for all applications of 2400 rated volts and higher.
Connection to the resistor incoming (and grounding if required) shall be via an enclosure mounted porcelain entrance bushing. The bushing terminal shall be suitable for connection of the customer’s specified wire.
Resistor Mounting

When specified, a free standing mounting stand shall be provided that is fabricated entirely from copper free aluminum. The stand shall have provisions for mounting/securing to a level concrete pad.

Grounding
Provisions shall be made to terminate the user’s 2/0 AWG copper ground wire on the mounting stand and the resistor safety enclosure for low resistance ground resistor assemblies.
Provisions shall be made to terminate the user’s number 2 AWG copper ground wire on the resistor safety enclosure for high resistance ground resistor assemblies.
Current Transformer
When specified for low resistance ground resistor assemblies a current transformer rated 600/5 shall be provided. The secondary leads shall be wired out to a NEMA 4x stainless steel junction box mounted on the outside of the safety enclosure and contain a CT shorting type terminal block.
Current transformers shall fully comply with ANSI/IEEE C57.13 and be suitable for protective relay applications.
Current transformers shall be a weatherproof butyl–molded type (or equivalent) suitable for use outdoors in an environment typical of that found in petrochemical facilities.
The voltage rating of the current transformer shall be rated for the specified line to line system voltage.

5.7 Nameplates

Individual nameplates shall be affixed to each resistor assembly supplied. The nameplate shall be made of stainless steel and contain all the information specified in ANSI/IEEE Std 32.

TESTING

The Manufacturer as a minimum shall perform all the tests required for neutral grounding resistors as outlined in ANSI/IEEE Std 32. The tests shall include:
Resistance Test: The DC resistance shall not vary more than ± 10 percent from the guaranteed value.
Applied potential test per ANSI/IEEE Std 32.
Check insulation resistance of resistor to frame and frame to safety enclosure with a 2500 VDC megohmeter.
Testing shall be done on completely assembled equipment.

When a witness test is specified the Owner shall witness the complete testing of all items detailed in Section 6.0 and special tests as indicated on the Data Sheets and contract documents.

DRAWINGS AND DATA REQUIREMENTS

All drawings provided for this equipment shall show equipment as specified and ordered. Typical drawings are not acceptable unless they are revised to show only the equipment being furnished. Drawings, test records, and manuals shall be supplied in the quantities and format as shown on the Data Sheets.

Information to be Supplied with Quotation
Specific listing of any exceptions to those requirements specified.
Equipment or features included but not necessarily specified.
Sketches showing equipment layout/orientation with dimensions.
Complete lists and descriptive data of all equipment and accessories proposed shall be included and any components not manufactured by the Seller submitting the proposal shall be so noted as well as the Manufacturer and type proposed.
Quote must be for equipment as specified, including any requested alternatives. Manufacturer recommended alternatives are encouraged and should be included in addition to the equipment as specified with separate cost adds/deducts.
Itemized list of unassembled equipment.
Cost for witness testing, if specified.
Information to be Submitted for Owner Approval after Receipt of Order
Complete Structural Drawings showing:
Dimensional plan and elevation, front view, and other elevation views if pertinent.
Conduit entrance locations and dimensions.
Incoming and outgoing cable terminator positions and type.
Purchaser’s wiring terminal block locations, and all other terminal block and wire termination locations.
Detailed Connection (Wiring) Diagrams showing:
All wiring within each unit.
Identification of all terminal blocks.
Clear identification, by some distinguishing method, of ALL wiring which is to be installed by Owner.
Complete CT information including saturation curves, physical dimensions, and wiring diagrams.
Certified Information to be Supplied
All information requested in paragraph 7.2.
Installation, Maintenance and Operating Instructions: Installation and operating instructions shall cover all the equipment furnished and include field testing methods, test levels and acceptance criteria for D.C.High–Potential Testing and Resistor Resistance Testing.

Material List: A material list shall be furnished listing the quantity, rating, type, and manufacturer’s catalog number of all equipment in each unit.
Test Reports for testing outlined in Section 6.0.

8.0 SPARE PARTS

Spare parts requirements are not applicable to this Practice.

SHIPPING

Preparation for Shipment shall be in accordance with Manufacturer’s standard, unless otherwise noted on the ‘Request for Quotation’ and/or Purchase Order. The Manufacturer shall be solely responsible for the adequacy of the ’Preparation for Shipment’ provisions employed in respect of materials and application, to provide materials to their destination in ex–works condition when handled by commercial carrier systems.
Each piece of equipment shipped separate shall be provided with a permanently–attached readily visible, identification tag.

10.0 TABLES

TABLE 1 TYPICAL RATINGS

Ampere	Duty	Voltage	Voltage	Insulation Class
		L–L	L–G
5.0 to 3.5(1)	Continuous	480	277	600 volt

NOTE:

(1) Resistors supplied with fault finding pulsating systems may have intermittent current pulses up to 7.5 ampere.

TABLE 2 TYPICAL RATINGS

Fault Ampere	Ohms	Duty Sec.	Voltage	Voltage	Insulator Class (volts)
			L–L	L–N
400	3.5	10	2,400	1,400	5000
400	6	10	4,160	2,400	5000
400	20	10	13,800	8,000	15,000
400	50	10	34,500	20,000	38,000

TABLE 3

CERTIFIED INFORMATION REQUIRED IN ELECTRONIC FORMAT for NEUTRAL GROUNDING RESISTORS

PER EP 13–10–1

Item	Description	Format	As–Built
1	Complete structural drawings per paragraph 7.2.1.	See EP 2-5-2	Yes
2	Detailed connection (wiring) diagrams per paragraph 7.2.2.	See EP 2-5-2	Yes
3	Complete information on any CT’s provided per paragraph 5.6 and 7.2.3.	See EP 2-5-2	Yes
4	Test reports per paragraph 6.0.	See EP 2-5-2	Yes
5	Installation, maintenance and operating instructions.	See EP 2-5-2	Yes
6	Material list of all material supplied per paragraph 7.3.3.	See EP 2-5-2	Yes

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