TAP/GATEWAY Communication Cable Types and Installation

Contents: 

1. TAP Communication Cable Requirements
2. Recommended Cable Types
3. Maximum Cable Length Recommendations
4. Using Ethernet Cables (Cat 5 / Cat 6)
5. Installation Tips!

Introduction

This article explains the technical requirements for the cable that connects the TAP (or Gateway), to the Data Logger (CCA, Cloud Connect or MMU). 

The TAP (Tigo Access Point) is a radio transceiver used in management of a monitored MLPE system. This device replaced the legacy Gateway. Both the TAP and Gateway are Access Points, but they use different wiring methods. To identify which one is installed on a system, see: TAP vs Gateway

Note: A TAP can replace a Gateway. (However, a gateway should not be used to replace a TAP).

TAP/Gateway Cable Requirements

The cable used to connect a TAP to the Data Logger must have these features:

• At least 1 Twisted Pair (TP) of wires (for A and B connections).
• Smallest supported wire size is 22 AWG (0.33 mm²) and largest is 18 AWG.
• Max cable Outside Diameter (OD) of 0.346 inches (so it will fit through the cable gland).

Always check with your Authority Having Jurisdiction (AHJ) for local wiring requirements, and check the product datasheet for exact and current specifications: TAP Datasheet

Recommended Cable Types

The distance (combined with the number of TAPS per CCA) greatly effects the voltage at the TAP(s). Tigo strongly recommends a cable type that is RS-485 compliant for wiring over 100 feet (from the Data Logger, to the most distant TAP). However, an Ethernet cable (of any Category) may be used for systems with 2 TAPs (or less).

• Conduit is recommended to avoid damage by animals.
• If the cable is not housed in a conduit, please use an outdoor-rated (UV resistant) cable.
• Can I run my TAP Communication Cable in the PV Array Conduit?

Many cables are manufactured in 2 shielding types:

• UTP - Unshielded Twisted Pair
• STP - Shielded Twisted Pair 

STP (shielded) cables are highly recommended when wiring path is in close proximity to electric motors (like those used in HVAC equipment), or other EMF sources like powerful radio transmitters, etc.

Compliant Cables:

The Belden 3107A meets the internal component requirements, and fits within the 9mm opening on the TAP. (for a full list, see: Belden's RS-485 offerings)

Non-Compliant Cables:

Ethernet Category 5e UTP, CMP (see: Using Ethernet Cables (CAT5 / CAT6))

Ethernet Category 5e, UTP, CMR (riser rated) (see: Using Ethernet Cables (CAT5 / CAT6))

Note: It is advised to only use Ethernet cables on systems that have a maximum of 2 TAPs and less than 100 feet to the farthest TAP.

Maximum Cable Length Table

• The length of a cable along with its wire sized determines its resistance.
• Longer cables have more resistance, naturally.

The table (below) provides the maximum length recommendations per cable type and number of TAPs.

1. Wire sizes are listed in American Wire Gauge (AWG) and Millimeters (mm).
2. Wire Lengths are listed in Feet (ft) and Meters (m). 

For commercial systems:

The use of Ethernet cables is strongly discouraged for Commercial applications, as these may have a higher data-corruption rate. Only RS-485 rated cables have the correct electrical characteristics for minimal  corruption between the Cloud Connect and TAP.

Using Ethernet Cables (Cat 5 / Cat 6)

1.  A and B signals:  Use 2-wire, from the same pair.
2. To minimize voltage drop extra pairs can be combined.
   (This can be helpful for distances over 100 feet, or on systems with 2 or more TAPs.)
3. The picture is using the pair color code of Blue, and White/Blue are used.

STEP 1 Use ONLY 22 AWG wires with the Insulation Displacement Connector (punch-down) terminal. Remove 1.5 inches of the outer jacket. Be careful to not nick or damage the insulation on the internal wires. If damage occurs, cut the cable-end off, and start over.
STEP 2.  Opening and Closing the TAP. The Red Arrow is pointing at the screw terminal connector which is used for 20 or 18 AWG sized wires. Note: This example has the required 120 ohm termination resistor across the A and B on the right hand sided, for the last TAP in a 'chain' of TAPS connected to a CCA.
STEP 3   Remove the Screw terminal connector by using a thin flat tool such as a screwdriver. Place it underneath the connector then rotate it clockwise, and then rotate it counter clockwise to loosen the connector from the pins on the circuit board.
STEP 4 Unscrew the Cable Gland Cap feed the cable through. This is easier to do before removing the outer jacket of the cable as instructed in (STEP 1).
STEP 5.1 Strip the outer jacket a length o 1.25 inches. Strip the wires 3/8 of an inch. If needed, loosen the screws until there is space for the wire(s). Insert the wires into the connector, and tighten them until a firm tug does not remove them. NOT so tight to cut/break the wire. Press the connector back on to the pins until it contacts the printed circuit board. This example is using Ethernet cable but RS-485 cables also may use this connector. Picture NOTE: Blue and white with a blue stripe used as the twisted pair for the A and B signals. Suggestion: take a picture or write down what color of the twisted-pair AND which  solid color is being used as A or B signal
STEP 5.2 (Using IDC Method) Remove outer jacket Lay the unstripped wires above their terminals Use a punch-down tool or small screwdriver, press the wire down until it is in the bottom of the notch. Note: Since the IDC connector cannot take multiple wires, the maximum wire length is affected and limiting the number of TAPS to 2.
STEP 6 Tighten the Cable Gland, by turning it clockwise (righty tighty). Make sure it's firmly tightened, to prevent water entry. Close the TAP cover Clip TAP to the frame of a PV module. Make sure the cable and gland are pointing so gravity causes water to drip away, and not towards the gland.

Installation Tips:

Conduit and Cable Trays also having the gateway cable: 

When running the communication cable in the same conduit as an PV String Wire (home-run string wires), use a cable that has at least 600 VDC insulation or matching the inverter maximum string VDC rating.

• This eliminates the need for installation of a separate conduit for the communication cable, assuming the string voltage will never exceed 600 VDC.
• Ethernet cable is normally rated to only 300 VDC.

Termination resistor

A resistor is pre-installed on the right-hand side terminals on each TAP. It is connected to the A and B terminals, which are the RS-485 data signals. Remove the resistors from the other TAPs along the daisy-chain. The last TAP in the chain, it must have the resistor inserted in the outgoing A and B terminals.

Mounting the TAP:

1. The TAP is designed to be installed under a panel (hidden from direct sunlight).
2. The TAP installs to the PV-Module frame using the mounting clips.
3. Mount the TAP with the label side outward (facing away from the panel).
4. If the PV-Module has no frame, the clips on the TAP can be removed. The remaining holes can be used for screw-mounting them to a racking system.
5. Mount the TAP in a centrally located area, as the radio distribution has a radial circumference.
6. Radio signal obstructions, including opposing roof angles, drop-roofs, dormers, gables and different levels of panels, etc., require individual TAPS, in nearly all cases. 

Warning: Do not mount the TAP inside an attic. Material such as roofing, insulation, sheathing and shingles, can present a physical barrier to the signal.

For complete installation directions, see page 12 of the TAP Installation Manual, and feel free to consult with a Tigo Energy Sales Engineer for any questions.

Testing communications with TAPs: 

After installation is complete, the Discovery portion of the commissioning process should find all of the TAPs, quickly.If the Discovery reports fewer TAPs than configured on the Equipment page, run a TAP Test.

For legacy equipment (Tigo Cloud Connect and MMU), run a Gateway test